Alternatives to Sumproduct(Sumif( for use with closed workbook

Well, I'm back. Yesterday I had posted a potential formula of:
=SUMPRODUCT((--(A2:A31=F8))+(--(A2:A31=F9))+(--(A2:A31=F10)),C2:C31)

The A2:A31 will actually reside in another workbook, that preferably will be closed. I needed a way to set the F8:F10 more dynamically (with offset by match(true(isblank ) so it was suggest the above could be rewritten as:
=SUMPRODUCT(SUMIF(A2:A31,F8:F10,C2:C31))

That latter formula is pure genius. Until I realized it can't be used on a closed workbook. In this latter one, A2:A31 and C2:C31 will be a closed workbook, and F8:F10 will change dynamically, making the first formula out of the question as well.

Is there any way to have the best of both worlds? The alternative, obviously, is to move the data in the closed workbook to the current workbooks (yes, all seven of them). Perhaps I can populate those second sheets with formulas in case the underlying data changes (which is my concern, though it may ultimately be unlikely the data changes).