Find last value within date range

Anonymous 
If you haven't shared the file, I wouldn't in a milion years figure out that in fact the Dates in the Product Table are in 2022 while the Dates in the Transaction Table are in 2018. The Dates in the Product Table do not even exist in the Date table! I was about to go crazy woundering why The Product Table do not exist inside the matrix even if the three months are were selected. 

Please refer to your sample file amended with the solution

Prod Descr = 
VAR Currentprod =
    SELECTEDVALUE ('TransactionTable'[ProductID])
VAR T1 =
    CALCULATETABLE ( 
        ProductTable,
        ALL ( DateTable ),
        ProductTable[ProductID] = Currentprod,
        MONTH ( ProductTable[Date] ) <= MONTH ( MAX ( DateTable[Date] ) )
    )
VAR T2 =
    TOPN ( 1, T1, ProductTable[Date] )
VAR Result =
    MAXX ( T2, ProductTable[Product Description] )
RETURN
    Result