thats exactly it, and Im guessing if I wanted to make the 10 week a variable I just edit

=IFERROR(SUM(OFFSET(A1,MATCH(A11,A2:A8,0),MATCH(A12,1:1,0)-1,,10)),"NO")

to

=IFERROR(SUM(OFFSET(A1,MATCH(A11,A2:A8,0),MATCH(A12,1:1,0)-1,,@@)),"NO") where @@ becomes the cell with the variable

Moo your spot on - nicely done and clean - Ill have anther question later but for now - its put the kid to bed time!!