Excel 2003

I have a total sheet that gets data from three different shift sheets (all
in the same workbook) for a monthly report. I have named ranges on each
shift sheet for each month's production data (S1M1, S1M2, S1M3, S2M1...)
where S1M1 =A2:AC147, S1M2 = A148:AC329, etc. The old formula
was:=SUMIF('SHIFT 1'!$L$1:$L$147,"BB",'SHIFT 1'!$T$1:$T$147). I'm stumped as
to what the new formula would be - how would I direct Excel to column L of
S1M1 to search for "BB", then add the contents of column T? The range
changes each month, and I thought it would be better to change the name range
monthly, rather than the cells in 100+ formulas.

TIA
Carole O