Working with date ranges to find initial install date count

Hi mattyj2009 

You may add index first and then create columns and measures as below.Attached sample file for your reference.

Last_DisconnectDate = 
VAR last_Dis_date =
    CALCULATE (
        MAX ( Data[Disconnect Date] ),
        FILTER (
            ALLEXCEPT ( Data, Data[Address ID] ),
            Data[Index]
                = EARLIER ( Data[Index] ) - 1
        )
    )
RETURN
    IF ( last_Dis_date = BLANK (), Data[Disconnect Date], last_Dis_date )

New_index = IF(Data[Install Date]>Data[Last_DisconnectDate],Data[Index],0)

Count = 
VAR min_date =
    CALCULATE (
        MIN ( Data[Install Date] ),
        FILTER (
            ALL ( Data ),
            Data[Address ID] = MAX ( Data[Address ID] )
                && Data[New_index] = MAX ( Data[New_index] )
        )
    )
RETURN
    CALCULATE (
        DISTINCTCOUNT ( Data[Address ID] ),
        FILTER ( Data, IF ( Data[Install Date] = min_date, 1 ) )
    )

CountSum = SUMX(VALUES(Data[Install Date]),[Count])

Regards,