VLookup Verification

[jallain]

OK, sorry to be so vague on this, but I'm hoping you guys can help me out.

For my work, I have a list of over 500 model numbers, and I grab costs from various vendors every week. I create sheets for each of the vendors, and use the VLOOKUP function to populate the field. The issue is that I've got no way to verify if I have all model numbers accounted for in my sheets, other than printing up to 10 lists of over 300 model numbers and checking them against my master list, really time consuming!

I was wondering if there was a way to create a VLOOKUP function, or some conditional formatting, that would somehow tell me which cells from my secondary sheets were pulled into the main sheet? The problem I have is that the cells are locked and formulas are hidden and all that stuff in my master sheet due to a slew of outside variables.

I've included a sample sheet to give you a small snapshot of what I'm looking at.

Hopefully I wasn't too vague, and you guys are understanding what I'm trying to do.