Well, that's the pits! I copied the formula directly fro the spreadsheet and it gives me zero. I did
=SUMPRODUCT(Q74:Q91)
Q74:Q91 is where I did the fill down to see that the extract was working properly. The SUMPRODUCT above gave me 84, which is correct.
The items to be summed are all entered from the keyboard, so they are not computed. I've got Office 2011 on my Mac. Is that the issue?