Cummulative Prev Change

Hi Anonymous 
The solution at this point is two columns.


Let me know if you have any questions.

If this solves your issues, please mark it as the solution, so that others can find it easily. Kudos are nice too.
Nathaniel

Cumulative = 

var _curIndex =PA_KEY[Index]
var _minIndex = CALCULATE(MIN(PA_KEY[Index]),ALLEXCEPT(PA_KEY,PA_KEY[PA#]),PA_KEY[Index]<_curIndex)

return

IF(_curIndex = _minIndex || _curIndex = _minIndex+1,BLANK(), CALCULATE(sum(PA_KEY[RequestedValue]),ALLEXCEPT(PA_KEY,PA_KEY[PA#]),PA_KEY[Index]=_curIndex -1))

Cumulative and previous = 
VAR _curIndex = PA_KEY[Index]   //Get current Index from this row
VAR _minIndex = CALCULATE ( MIN ( PA_KEY[Index] ), ALLEXCEPT ( PA_KEY, PA_KEY[PA#] ), PA_KEY[Index] < _curIndex )    //Get minimum index for this PA#                                
                              
VAR _prev3 = CALCULATE ( SUM ( PA_KEY[Cumulative] ),  ALLEXCEPT ( PA_KEY, PA_KEY[PA#] ), PA_KEY[Index] = _curIndex - 1 )   // Get the previous row amount from the Cumulative column                                

RETURN
    IF (                                        //Return a blank if the current index is equal to the first two rows of this PA# else do the calc and add the previous row from the Cumulative column
        _curIndex = _minIndex
            || _curIndex = _minIndex + 1,
        BLANK (),
        CALCULATE (
            SUM ( PA_KEY[RequestedValue] ),
            ALLEXCEPT (
                PA_KEY,
                PA_KEY[PA#]
            ),
            PA_KEY[Index] = _curIndex - 1
        ) + _prev3
    )

Anonymous 

Just this portion is the measure and it relies on the index column Nathaniel_C  added to your sample table.  

Column = 
VAR _MinIndex = CALCULATE ( MIN ( PA_KEY[Index] ), ALLEXCEPT ( PA_KEY, PA_KEY[PA#] ) )
VAR _RowIndex = [Index]
RETURN CALCULATE ( SUM ( PA_KEY[RequestedValue] ), ALLEXCEPT ( PA_KEY, PA_KEY[PA#] ), PA_KEY[Index] > _MinIndex && PA_KEY[Index] < _RowIndex )

 Are you able to add an index column to your source data that will properly order the lines?

The problem with using the original table is you don't know what order the lines are going to come in unless you give it an order by.  You could add the index on the SQL side as well, something like this.

SELECT
	PA_Key,
	Version,
	[Invoice LINE],
	CONTRACTLINEVALUE,
	REQUESTEDVALUE,
	PA#,
	ROW_NUMBER() OVER( ORDER BY ( SELECT 0 ) ) AS RowIndex
FROM Table
ORDER BY
	PA_Key,
	Version,
	[Invoice LINE]