Lookup Matching Names in Multiple Columns

Hello, I found this site on a google search. Thanks in advance for any help that could possibly be provided.

I'm an IT PM. I currently have spreadsheet - column A consists of 1300 user account names. That's my base. Columns B thru L are individual application groups containing the user account names for each group. So column B could have 600 account names, Column C-2000 account names, D-2400 account names, etc. I think you understand what I'm getting at here.

I need to see if any user account name in column A, exists in any of the columns B thru L. If so, that user cannot be upgraded.

Can anyone tell me how to automate that?

THANK YOU VERY MUCH IN ADVANCE!!

Regards,
Jeff