Index / Match to find value at point of intersection across multiple sheets

Hi. Pleas help
I am using the Index and Match functions to obtain the value at the point of intersection of two numbers, I can obtain the value from 2 sheets only, some how I cannot get the formular to work for the rest of the sheets.

I don't think this can be done in a single formula. I've added some additional columns (which can be hidden, or moved elsewhere on the sheet) - would that do you?

Andrew
Thanks, but when I enter new part numbers for any of the sheets, the values change to -99, I am not sure if i defined my problem clearly. This is what I am looking for: When I enter two part nos. in the required field, I must obtain the value at the point of intersection of those patr nos, the formular should lookup Sheet2 and if it does not find it, it should look in the next sheet and so on.
Thanks in advance.
Pipes

That's what my formula are doing - if they return -99 it means that the combination hasn't been found. When you add new part numbers are you updating the ranges that it's looking in?

Andrew
I made changes to the cell refference,for the lookup value and it works perfectly. Thanks once again, you have been a great help.