INDEX with column by column instead of row by column

May have to use a VLookup here, but I'm not really sure how to handle this in a VLookup. I have a few sheets that contain the same info in columns A and B. This info may not be in EVERY sheet, but I'd like Excel to look at every sheet and check. If cell A2 matches something in A:A in another sheet, AND B2 in the first sheet matches something in B:B in the second sheet, return whatever is in column C of that row. Row numbers of the same info may not match. For example, info1 may be in Row 45 of sheet1, and row 3 of sheet2, and row 500 of sheet 3 etc.

If the INDEX function is able to do a match on two columns rather than a row and a column, that would work too. As I know it though, INDEX finds the cross of a row by column, and so right now it doesn't quite work for this application.

This is, without exaggeration, the hardest lookup problem I've yet seen on this forum. Like, I think it's theoretically solvable with lookups, but the formula I'm imagining are... intimidating.

How many sheets is "every sheet"? If it's more than, like, four, OR if it can change, you're pushing yourself towards using some VBA.
Are you looking for the FIRST match or ALL matches? If it's more than the first match, you're better off doing some kind of tabling operation instead.

Broadly, my response is this:
1) Move the data onto one sheet, not multiple sheets
2) Can you use a PivotTable to explore the data instead?
--You can get away with multiple sheets if you use the PowerPivot addon

I just saw your responses, hehe. Sorry, I actually typed up a solution to post and then I got sidetracked with work.

@ben: There's 3 sheets of data, and a cover sheet that pulls this data from the three sheets. I cannot move the data to one sheet because it would be unmanageable for my co-workers. There's separate sheets for a reason Unfortunately, I'm not too savvy with pivot tables although I have heard a lot of testimonies about their usefulness.

@JBeaucaire: 4 sheets total. Match only occurs once PER SHEET. If info1A is in column A of sheet 1, and info1B is in column B of sheet 1, then there will not be an info1A and info1B again on sheet 1. But, it MIGHT be in sheets 2 or 3 or 4.

I would like to post the workbook but I'm currently testing my proposed solution with real data, some of which contains sensitive info. Let me know if you don't understand my solution and I'll indulge your curiosity if you like

That's substantially easier than I first thought.

If there's one-and-only-one match per sheet, then you can just use SUMPRODUCT to do the matching.

=SUMPRODUCT(--(A:A = A_in), --(B:B = B_in), ROW(A:A) )

that will return the sum of all rows where both A & B match, which will be the matching row in a one-and-only-one scenario.

Feed that into an INDEX and you're good:

=INDEX(C:C, row)

If it's three sheets, my advice is just return the matches (or errors in the case of no matches) for all three sheets.

I actually used a SUMPRODUCT in another similar application, and it was such a complex formula that it slowed down my whole workbook, and so I avoided it this time around But for something like this, it might work nicely.