duplicate, yes/no, in a table

HI and happy holidays to all.
see attached sample. (i hope it loads)

I need to find duplicates as related to columns a & b in a table. Column b is named "rev active".
However, my formula is missing something.
It will return YES as long as the duplicates are in adjacent cells...i.e. a3 and b3.
i need to know if a99 duplicated anywhere in column b, not just cell b99.

<<IF(A2=[@[rev active]],"YES","NO")>>

What did I miss?
Thank you in advance.