|Your offsetting everything, so you need to compensate.|
Your INDEX array does not match the physical cell locations.
Your array is C1 : QW51
Your first match doesn't start until row 4: MATCH(F6,Sheet8!C4:C51,0)
so you need to compensate by adding 3 to the match
so you get the correct physical row number, not the array row number.
That's the point DERBYDAD03 was making with:
the value was actually found at the intersection of Row 3, Column 4 of the lookup_array used by the INDEX function.
Same with the column match, your not starting until column K: MATCH(F4,Sheet3!K1:QW1,0)
so you need to add 8 to you get the correct column number,
your array starts at column C so
plus 1 to get the next column over,
So your formula should look something like: