How to automatic rolling data based on the change of the date

Hi Guy,

Currently I'm creating a rolling 12 month forecast in excel. I'm using the sumif formula to pick up the data in the column that matched to the select month:

SUMIF($A:$A,$T10,OFFSET('RJV FY2013 Op B'!$A$1,0,COLUMN('Rolling Cashflow'!D$8))).

However, if I change the date in D8 from Jun12 to July12, the formula is still picking up the Jun12 data instead of Jul12. How should I fix up this?

Thanks,
YS