Ok... so I've tried doing this every which way I can think of. I have
multiple spreadsheets that I need to have looked at to verify that the
account numbers do not show on any other spreadsheet. Most of the
spreadsheets are in seperate workbooks. Here are two of the more detailed
functions I've tried:

1. =IF(ISERROR(VLOOKUP(Q2,'[CERTS, DRGS & ADRS.xls]Old
CERTs'!$C:$C,1,FALSE)),"",IF(VLOOKUP(Q2,'[CERTS, DRGS & ADRS.xls]Old
CERTs'!$C:$C,1,FALSE),"yes",IF(ISERROR(VLOOKUP(Q2, '[CERTS, DRGS &
ADRS.xls]A-K'!$O:$O,1,FALSE)),"",IF(VLOOKUP(Q2,'[CERTS, DRGS &
ADRS.xls]A-K'!$O:$O,1,FALSE),"yes",IF(ISERROR(VLOOKUP(Q2,'[CERTS, DRGS &
ADRS.xls]L-Z'!$O:$O,1,FALSE)),"",IF(VLOOKUP(Q2,'[CERTS, DRGS &
ADRS.xls]L-Z'!$O:$O,1,FALSE),"yes",""))))))

2. =IF(VLOOKUP(Q2,'[CERTS, DRGS & ADRS.xls]Old
CERTs'!$C:$C,1,FALSE),"yes",IF(ISERROR(VLOOKUP(Q2, '[CERTS, DRGS &
ADRS.xls]Old CERTs'!$C:$C,1,FALSE)),"",IF(VLOOKUP(Q2,'[CERTS, DRGS &
ADRS.xls]A-K'!$O:$O,1,FALSE),"yes",IF(ISERROR(VLOOKUP(Q2,'[CERTS, DRGS &
ADRS.xls]A-K'!$O:$O,1,FALSE)),"",IF(VLOOKUP(Q2,'[CERTS, DRGS &
ADRS.xls]L-Z'!$O:$O,1,FALSE),"yes",IF(ISERROR(VLOOKUP(Q2,'[CERTS, DRGS &
ADRS.xls]L-Z'!$O:$O,1,FALSE)),"",""))))))

Any help would be greatly appreciated.