Thanks for your help and input - using some of your examples and a lot debug, I was able to achieve the result I was looking for. It did lead to a rather large formula but appears to be working great:

=IF(MONTH($A$17)=1,0,SUM(B2:INDEX(named_range,MATC H(TEXT($A$17,"mmm"),A2:A13,0)-1,32)))+SUM(OFFSET($A$1,MATCH(TEXT($A$17,"mmm"),$A $1:$A$13, 0)-1,1,1,MATCH(DAY($A$17),$A$1:$AF$1,0)-2))

Thanks again.