Add items with different latest dates

I figured it out.

But, if someone knows a better way than all of the manual iterations, I'm all ears.

LastTotalDTLevel = 
	VAR IBXID =
		LOOKUPVALUE ( 
			IBXs[IBX_ID], 
			IBXs[IBX_Name], 
			SELECTEDVALUE ( IBXs[IBX_Name] ) 
		)
    VAR DT1 =
        LOOKUPVALUE (
            Tanks[fk_GeneratorName_ID],
            Tanks[INDEX],
            1,
            Tanks[fk_IBX_ID],
            IBXID,
            Tanks[Day_Tank],
            TRUE ()
        )
	VAR DT1Date =
        CALCULATE (
            LASTDATE (
                RunData[RunData_Date]
            ),
            ALLEXCEPT (
                RunData,
                RunData[fk_GeneratorName_ID]
            ),
            RunData[fk_GeneratorName_ID] = DT1
        )
    VAR Run1 =
        LOOKUPVALUE (
            RunData[RunData_ID],
            RunData[fk_IBX_ID],
            IBXID,
            RunData[fk_GeneratorName_ID],
            DT1,
            RunData[RunData_Date],
            DT1Date
        )
    VAR DT2 =
        LOOKUPVALUE (
            Tanks[fk_GeneratorName_ID],
            Tanks[INDEX],
            2,
            Tanks[fk_IBX_ID],
            IBXID,
            Tanks[Day_Tank],
            TRUE ()
        )
	VAR DT2Date =
        CALCULATE (
            LASTDATE (
                RunData[RunData_Date]
            ),
            ALLEXCEPT (
                RunData,
                RunData[fk_GeneratorName_ID]
            ),
            RunData[fk_GeneratorName_ID] = DT2
        )
    VAR Run2 =
        LOOKUPVALUE (
            RunData[RunData_ID],
            RunData[fk_IBX_ID],
            IBXID,
            RunData[fk_GeneratorName_ID],
            DT2,
            RunData[RunData_Date],
            DT2Date
        )
    VAR DT3 =
        LOOKUPVALUE (
            Tanks[fk_GeneratorName_ID],
            Tanks[INDEX],
            3,
            Tanks[fk_IBX_ID],
            IBXID,
            Tanks[Day_Tank],
            TRUE ()
        )
	VAR DT3Date =
        CALCULATE (
            LASTDATE (
                RunData[RunData_Date]
            ),
            ALLEXCEPT (
                RunData,
                RunData[fk_GeneratorName_ID]
            ),
            RunData[fk_GeneratorName_ID] = DT3
        )
    VAR Run3 =
        LOOKUPVALUE (
            RunData[RunData_ID],
            RunData[fk_IBX_ID],
            IBXID,
            RunData[fk_GeneratorName_ID],
            DT3,
            RunData[RunData_Date],
            DT3Date
        )
    VAR DT4 =
        LOOKUPVALUE (
            Tanks[fk_GeneratorName_ID],
            Tanks[INDEX],
            4,
            Tanks[fk_IBX_ID],
            IBXID,
            Tanks[Day_Tank],
            TRUE ()
        )
	VAR DT4Date =
        CALCULATE (
            LASTDATE (
                RunData[RunData_Date]
            ),
            ALLEXCEPT (
                RunData,
                RunData[fk_GeneratorName_ID]
            ),
            RunData[fk_GeneratorName_ID] = DT4
        )
    VAR Run4 =
        LOOKUPVALUE (
            RunData[RunData_ID],
            RunData[fk_IBX_ID],
            IBXID,
            RunData[fk_GeneratorName_ID],
            DT4,
            RunData[RunData_Date],
            DT4Date
        )
    VAR DT5 =
        LOOKUPVALUE (
            Tanks[fk_GeneratorName_ID],
            Tanks[INDEX],
            5,
            Tanks[fk_IBX_ID],
            IBXID,
            Tanks[Day_Tank],
            TRUE ()
        )
	VAR DT5Date =
        CALCULATE (
            LASTDATE (
                RunData[RunData_Date]
            ),
            ALLEXCEPT (
                RunData,
                RunData[fk_GeneratorName_ID]
            ),
            RunData[fk_GeneratorName_ID] = DT5
        )
    VAR Run5 =
        LOOKUPVALUE (
            RunData[RunData_ID],
            RunData[fk_IBX_ID],
            IBXID,
            RunData[fk_GeneratorName_ID],
            DT5,
            RunData[RunData_Date],
            DT5Date
        )
    VAR DT6 =
        LOOKUPVALUE (
            Tanks[fk_GeneratorName_ID],
            Tanks[INDEX],
            6,
            Tanks[fk_IBX_ID],
            IBXID,
            Tanks[Day_Tank],
            TRUE ()
        )
	VAR DT6Date =
        CALCULATE (
            LASTDATE (
                RunData[RunData_Date]
            ),
            ALLEXCEPT (
                RunData,
                RunData[fk_GeneratorName_ID]
            ),
            RunData[fk_GeneratorName_ID] = DT6
        )
    VAR Run6 =
        LOOKUPVALUE (
            RunData[RunData_ID],
            RunData[fk_IBX_ID],
            IBXID,
            RunData[fk_GeneratorName_ID],
            DT6,
            RunData[RunData_Date],
            DT6Date
        )
    VAR DT7 =
        LOOKUPVALUE (
            Tanks[fk_GeneratorName_ID],
            Tanks[INDEX],
            7,
            Tanks[fk_IBX_ID],
            IBXID,
            Tanks[Day_Tank],
            TRUE ()
        )
	VAR DT7Date =
        CALCULATE (
            LASTDATE (
                RunData[RunData_Date]
            ),
            ALLEXCEPT (
                RunData,
                RunData[fk_GeneratorName_ID]
            ),
            RunData[fk_GeneratorName_ID] = DT7
        )
    VAR Run7 =
        LOOKUPVALUE (
            RunData[RunData_ID],
            RunData[fk_IBX_ID],
            IBXID,
            RunData[fk_GeneratorName_ID],
            DT7,
            RunData[RunData_Date],
            DT7Date
        )
    VAR DT8 =
        LOOKUPVALUE (
            Tanks[fk_GeneratorName_ID],
            Tanks[INDEX],
            8,
            Tanks[fk_IBX_ID],
            IBXID,
            Tanks[Day_Tank],
            TRUE ()
        )
	VAR DT8Date =
        CALCULATE (
            LASTDATE (
                RunData[RunData_Date]
            ),
            ALLEXCEPT (
                RunData,
                RunData[fk_GeneratorName_ID]
            ),
            RunData[fk_GeneratorName_ID] = DT8
        )
    VAR Run8 =
        LOOKUPVALUE (
            RunData[RunData_ID],
            RunData[fk_IBX_ID],
            IBXID,
            RunData[fk_GeneratorName_ID],
            DT8,
            RunData[RunData_Date],
            DT8Date
        )
    VAR DT9 =
        LOOKUPVALUE (
            Tanks[fk_GeneratorName_ID],
            Tanks[INDEX],
            9,
            Tanks[fk_IBX_ID],
            IBXID,
            Tanks[Day_Tank],
            TRUE ()
        )
	VAR DT9Date =
        CALCULATE (
            LASTDATE (
                RunData[RunData_Date]
            ),
            ALLEXCEPT (
                RunData,
                RunData[fk_GeneratorName_ID]
            ),
            RunData[fk_GeneratorName_ID] = DT9
        )
    VAR Run9 =
        LOOKUPVALUE (
            RunData[RunData_ID],
            RunData[fk_IBX_ID],
            IBXID,
            RunData[fk_GeneratorName_ID],
            DT9,
            RunData[RunData_Date],
            DT9Date
        )
    VAR DT10 =
        LOOKUPVALUE (
            Tanks[fk_GeneratorName_ID],
            Tanks[INDEX],
            10,
            Tanks[fk_IBX_ID],
            IBXID,
            Tanks[Day_Tank],
            TRUE ()
        )
	VAR DT10Date =
        CALCULATE (
            LASTDATE (
                RunData[RunData_Date]
            ),
            ALLEXCEPT (
                RunData,
                RunData[fk_GeneratorName_ID]
            ),
            RunData[fk_GeneratorName_ID] = DT10
        )
    VAR Run10 =
        LOOKUPVALUE (
            RunData[RunData_ID],
            RunData[fk_IBX_ID],
            IBXID,
            RunData[fk_GeneratorName_ID],
            DT10,
            RunData[RunData_Date],
            DT10Date
        )
    VAR DT11 =
        LOOKUPVALUE (
            Tanks[fk_GeneratorName_ID],
            Tanks[INDEX],
            11,
            Tanks[fk_IBX_ID],
            IBXID,
            Tanks[Day_Tank],
            TRUE ()
        )
	VAR DT11Date =
        CALCULATE (
            LASTDATE (
                RunData[RunData_Date]
            ),
            ALLEXCEPT (
                RunData,
                RunData[fk_GeneratorName_ID]
            ),
            RunData[fk_GeneratorName_ID] = DT11
        )
    VAR Run11 =
        LOOKUPVALUE (
            RunData[RunData_ID],
            RunData[fk_IBX_ID],
            IBXID,
            RunData[fk_GeneratorName_ID],
            DT11,
            RunData[RunData_Date],
            DT11Date
        )
    VAR DT12 =
        LOOKUPVALUE (
            Tanks[fk_GeneratorName_ID],
            Tanks[INDEX],
            12,
            Tanks[fk_IBX_ID],
            IBXID,
            Tanks[Day_Tank],
            TRUE ()
        )
	VAR DT12Date =
        CALCULATE (
            LASTDATE (
                RunData[RunData_Date]
            ),
            ALLEXCEPT (
                RunData,
                RunData[fk_GeneratorName_ID]
            ),
            RunData[fk_GeneratorName_ID] = DT12
        )
    VAR Run12 =
        LOOKUPVALUE (
            RunData[RunData_ID],
            RunData[fk_IBX_ID],
            IBXID,
            RunData[fk_GeneratorName_ID],
            DT12,
            RunData[RunData_Date],
            DT12Date
        )
    VAR DT13 =
        LOOKUPVALUE (
            Tanks[fk_GeneratorName_ID],
            Tanks[INDEX],
            13,
            Tanks[fk_IBX_ID],
            IBXID,
            Tanks[Day_Tank],
            TRUE ()
        )
	VAR DT13Date =
        CALCULATE (
            LASTDATE (
                RunData[RunData_Date]
            ),
            ALLEXCEPT (
                RunData,
                RunData[fk_GeneratorName_ID]
            ),
            RunData[fk_GeneratorName_ID] = DT13
        )
    VAR Run13 =
        LOOKUPVALUE (
            RunData[RunData_ID],
            RunData[fk_IBX_ID],
            IBXID,
            RunData[fk_GeneratorName_ID],
            DT13,
            RunData[RunData_Date],
            DT13Date
        )
    VAR DT14 =
        LOOKUPVALUE (
            Tanks[fk_GeneratorName_ID],
            Tanks[INDEX],
            14,
            Tanks[fk_IBX_ID],
            IBXID,
            Tanks[Day_Tank],
            TRUE ()
        )
	VAR DT14Date =
        CALCULATE (
            LASTDATE (
                RunData[RunData_Date]
            ),
            ALLEXCEPT (
                RunData,
                RunData[fk_GeneratorName_ID]
            ),
            RunData[fk_GeneratorName_ID] = DT14
        )
    VAR Run14 =
        LOOKUPVALUE (
            RunData[RunData_ID],
            RunData[fk_IBX_ID],
            IBXID,
            RunData[fk_GeneratorName_ID],
            DT14,
            RunData[RunData_Date],
            DT14Date
        )
    VAR DT15 =
        LOOKUPVALUE (
            Tanks[fk_GeneratorName_ID],
            Tanks[INDEX],
            15,
            Tanks[fk_IBX_ID],
            IBXID,
            Tanks[Day_Tank],
            TRUE ()
        )
	VAR DT15Date =
        CALCULATE (
            LASTDATE (
                RunData[RunData_Date]
            ),
            ALLEXCEPT (
                RunData,
                RunData[fk_GeneratorName_ID]
            ),
            RunData[fk_GeneratorName_ID] = DT15
        )
    VAR Run15 =
        LOOKUPVALUE (
            RunData[RunData_ID],
            RunData[fk_IBX_ID],
            IBXID,
            RunData[fk_GeneratorName_ID],
            DT15,
            RunData[RunData_Date],
            DT15Date
        )
    VAR DT16 =
        LOOKUPVALUE (
            Tanks[fk_GeneratorName_ID],
            Tanks[INDEX],
            16,
            Tanks[fk_IBX_ID],
            IBXID,
            Tanks[Day_Tank],
            TRUE ()
        )
	VAR DT16Date =
        CALCULATE (
            LASTDATE (
                RunData[RunData_Date]
            ),
            ALLEXCEPT (
                RunData,
                RunData[fk_GeneratorName_ID]
            ),
            RunData[fk_GeneratorName_ID] = DT16
        )
    VAR Run16 =
        LOOKUPVALUE (
            RunData[RunData_ID],
            RunData[fk_IBX_ID],
            IBXID,
            RunData[fk_GeneratorName_ID],
            DT16,
            RunData[RunData_Date],
            DT16Date
        )
    VAR DT17 =
        LOOKUPVALUE (
            Tanks[fk_GeneratorName_ID],
            Tanks[INDEX],
            17,
            Tanks[fk_IBX_ID],
            IBXID,
            Tanks[Day_Tank],
            TRUE ()
        )
	VAR DT17Date =
        CALCULATE (
            LASTDATE (
                RunData[RunData_Date]
            ),
            ALLEXCEPT (
                RunData,
                RunData[fk_GeneratorName_ID]
            ),
            RunData[fk_GeneratorName_ID] = DT17
        )
    VAR Run17 =
        LOOKUPVALUE (
            RunData[RunData_ID],
            RunData[fk_IBX_ID],
            IBXID,
            RunData[fk_GeneratorName_ID],
            DT17,
            RunData[RunData_Date],
            DT17Date
        )
    VAR DT18 =
        LOOKUPVALUE (
            Tanks[fk_GeneratorName_ID],
            Tanks[INDEX],
            18,
            Tanks[fk_IBX_ID],
            IBXID,
            Tanks[Day_Tank],
            TRUE ()
        )
	VAR DT18Date =
        CALCULATE (
            LASTDATE (
                RunData[RunData_Date]
            ),
            ALLEXCEPT (
                RunData,
                RunData[fk_GeneratorName_ID]
            ),
            RunData[fk_GeneratorName_ID] = DT18
        )
    VAR Run18 =
        LOOKUPVALUE (
            RunData[RunData_ID],
            RunData[fk_IBX_ID],
            IBXID,
            RunData[fk_GeneratorName_ID],
            DT18,
            RunData[RunData_Date],
            DT18Date
        )
    VAR DT19 =
        LOOKUPVALUE (
            Tanks[fk_GeneratorName_ID],
            Tanks[INDEX],
            19,
            Tanks[fk_IBX_ID],
            IBXID,
            Tanks[Day_Tank],
            TRUE ()
        )
	VAR DT19Date =
        CALCULATE (
            LASTDATE (
                RunData[RunData_Date]
            ),
            ALLEXCEPT (
                RunData,
                RunData[fk_GeneratorName_ID]
            ),
            RunData[fk_GeneratorName_ID] = DT19
        )
    VAR Run19 =
        LOOKUPVALUE (
            RunData[RunData_ID],
            RunData[fk_IBX_ID],
            IBXID,
            RunData[fk_GeneratorName_ID],
            DT19,
            RunData[RunData_Date],
            DT19Date
        )
    VAR DT20 =
        LOOKUPVALUE (
            Tanks[fk_GeneratorName_ID],
            Tanks[INDEX],
            20,
            Tanks[fk_IBX_ID],
            IBXID,
            Tanks[Day_Tank],
            TRUE ()
        )
	VAR DT20Date =
        CALCULATE (
            LASTDATE (
                RunData[RunData_Date]
            ),
            ALLEXCEPT (
                RunData,
                RunData[fk_GeneratorName_ID]
            ),
            RunData[fk_GeneratorName_ID] = DT20
        )
    VAR Run20 =
        LOOKUPVALUE (
            RunData[RunData_ID],
            RunData[fk_IBX_ID],
            IBXID,
            RunData[fk_GeneratorName_ID],
            DT20,
            RunData[RunData_Date],
            DT20Date
        )
RETURN

	LOOKUPVALUE ( 
        RunData[DT_Level],
        RunData[RunData_ID],
        Run1
    )+
    LOOKUPVALUE ( 
        RunData[DT_Level],
        RunData[RunData_ID],
        Run2
    )+
    LOOKUPVALUE ( 
        RunData[DT_Level],
        RunData[RunData_ID],
        Run3
    )+
    LOOKUPVALUE ( 
        RunData[DT_Level],
        RunData[RunData_ID],
        Run4
    )+
    LOOKUPVALUE ( 
        RunData[DT_Level],
        RunData[RunData_ID],
        Run5
    )+
    LOOKUPVALUE ( 
        RunData[DT_Level],
        RunData[RunData_ID],
        Run6
    )+
    LOOKUPVALUE ( 
        RunData[DT_Level],
        RunData[RunData_ID],
        Run7
    )+
    LOOKUPVALUE ( 
        RunData[DT_Level],
        RunData[RunData_ID],
        Run8
    )+
    LOOKUPVALUE ( 
        RunData[DT_Level],
        RunData[RunData_ID],
        Run9
    )+
    LOOKUPVALUE ( 
        RunData[DT_Level],
        RunData[RunData_ID],
        Run10
    )+LOOKUPVALUE ( 
        RunData[DT_Level],
        RunData[RunData_ID],
        Run11
    )+
    LOOKUPVALUE ( 
        RunData[DT_Level],
        RunData[RunData_ID],
        Run12
    )+
    LOOKUPVALUE ( 
        RunData[DT_Level],
        RunData[RunData_ID],
        Run13
    )+
    LOOKUPVALUE ( 
        RunData[DT_Level],
        RunData[RunData_ID],
        Run14
    )+
    LOOKUPVALUE ( 
        RunData[DT_Level],
        RunData[RunData_ID],
        Run15
    )+
    LOOKUPVALUE ( 
        RunData[DT_Level],
        RunData[RunData_ID],
        Run16
    )+
    LOOKUPVALUE ( 
        RunData[DT_Level],
        RunData[RunData_ID],
        Run17
    )+
    LOOKUPVALUE ( 
        RunData[DT_Level],
        RunData[RunData_ID],
        Run18
    )+
    LOOKUPVALUE ( 
        RunData[DT_Level],
        RunData[RunData_ID],
        Run19
    )+
    LOOKUPVALUE ( 
        RunData[DT_Level],
        RunData[RunData_ID],
        Run20
    )