Excel formula for Bar-Code scanning old leased PCs to send back

Question

I have pallets of old machines that need to either be sold or, if listed as a currently leased machine, need to be sent back. Column A (A1:A90) includes all the leased PC Service Tags. Column C is where Service Tags are scanned and return with a YES or NO as to whether they are on Column A. I am using =IF(ISNA(VLOOKUP(E1, $A$1:$A$90,1)),"","Yes") but some Service Tags are returning a false-positive. With "Evaluate Formula" the false-positives are coming from the last Service Tag in Column A being used. Column A is being sorted in Ascending order. What can be done to correct this?

Answer 1

VLOOKUP(E1, $A$1:$A$90,1,FALSE)

Without FALSE, VLOOKUP will allow near matches -- which will give false positives.