Need my Rolling 12 function to reference a month in one cell but the year in another cell

[stacesil]

Currently My Rolling 12 formula is =SUM(OFFSET(Data!$D$6,0,MATCH($B$8,Data!$D$4:$ET$4,1)-1,1,-12)). Cell B8 is a date in the form of 'May-13'. I want the rolling 12 to recognize that month ONLY and for it to reference the year entered in another cell. Attached is a sample of my document, notice how when you change the years on the summary tab, everything auto changes and streams perfectly except for my rolling 12.

There is a comment in the document with simpler instructions..

Thank you!