Calculate Reduced balance quantity

So, perhaps you want something like the following:

Column = 
    VAR __PromiseDate = 'Table'[PROMISE DATE]
    VAR __SupplyDate = 'Table'[Supply_Date]
    VAR __TotalSoFar = 
        SUMX(
            FILTER(
                'Table',
                'Table'[Supply_Date] < EARLIER('Table'[Supply_Date])
            ),
            'Table'[ALLOTTED_QTY]
        )
    VAR __OrderQty = 
        SUMX(
            FILTER(
                'Table',
                'Table'[Demand_Order] = EARLIER('Table'[Demand_Order])
            ),
            'Table'[ORDER QTY]
        )
    VAR __PreText = 
        SWITCH(
            TRUE(),
            __TotalSoFar < __OrderQty,"Partial Quantity (" & 'Table'[ALLOTTED_QTY] & ") ",
            __TotalSoFar = __OrderQty,"Final Quantity (" & 'Table'[ALLOTTED_QTY] & ") ",
            BLANK()
        )
    VAR __PostText = 
        SWITCH(
            TRUE(),
            __SupplyDate < __PromiseDate,"Arriving Early on " & 'Table'[Supply_Date] & " for " & 'Table'[Demand_Order],
            __SupplyDate > __PromiseDate,"Arriving Late on " & 'Table'[Supply_Date] & " for " & 'Table'[Demand_Order],
            BLANK()
        )
RETURN
    __PreText & __PostText

PBIX is attached.

Try like

Cal remaining = sumx('Table','Table'[ORDER QTY])-sumx(filter('Table','Table'[ORDER-LINE]=EARLIER('Table'[ORDER-LINE]) && 'Table'[Supply_Date]<=EARLIER('Table'[Supply_Date])),'Table'[ALLOTTED_QTY])

Add additional filter like demand order if needed

Couple necessary fixes to the right supply date field and an equals sign. I think I got your change right as well, PBIX attached.

Column = 
    VAR __PromiseDate = 'Table'[PROMISE DATE]
    VAR __SupplyDate = 'Table'[SupplyDate]
    VAR __TotalSoFar = 
        SUMX(
            FILTER(
                'Table',
                'Table'[SupplyDate] <= EARLIER('Table'[SupplyDate]) &&
                    'Table'[ORDER-LINE] = EARLIER('Table'[ORDER-LINE])
            ),
            'Table'[ALLOTTED_QTY]
        )
    VAR __OrderQty = 
        SUMX(
            FILTER(
                'Table',
                'Table'[Demand_Order] = EARLIER('Table'[Demand_Order]) &&
                    'Table'[ORDER-LINE] = EARLIER('Table'[ORDER-LINE])
            ),
            'Table'[ORDER QTY]
        )
    VAR __PreText = 
        SWITCH(
            TRUE(),
            __TotalSoFar < __OrderQty,"Partial Quantity (" & 'Table'[ALLOTTED_QTY] & ") ",
            __TotalSoFar = __OrderQty,"Final Quantity (" & 'Table'[ALLOTTED_QTY] & ") ",
            BLANK()
        )
    VAR __PostText = 
        SWITCH(
            TRUE(),
            __SupplyDate < __PromiseDate,"Arriving Early on " & 'Table'[Supply_Date] & " for " & 'Table'[Demand_Order],
            __SupplyDate > __PromiseDate,"Arriving Late on " & 'Table'[Supply_Date] & " for " & 'Table'[Demand_Order],
            BLANK()
        )
RETURN
    IF(ISBLANK(__SupplyDate),[Supply_Date],__PreText & __PostText)