Try with the formula below which should work as long as you get the right condition logic based on your data set in where clause... I can not suggest any specific as there is no reference data here
=SUM([Measure]) in ( [Your dimension which being used for the block]) where ( (monthnumberofyear([Date])>= [month number dim] and Year([date]) = [Year Dimension] -1) or
(monthnumberofyear([Date])<= [month number dim] and Year([date]) = [Year Dimension]) )