I know i SHouldnt be able to write something here but, a same post was posted about that and the MOD My little Keldeo said:
It would be considered the same Unown, and therefore you couldn't use Farewell Letter again until your next turn. The catch here is that Unown is being moved from one public zone (your Discard Pile) to another (your Bench), and the game does keep track of cards in public zones (A public zone is a zone where cards are face up and visible to all players, such as in play, your Discard, etc.). This is different than a card putting Unown into a private zone such as with Buddy-Buddy Rescue (your hand) or Super Rod (your deck). Once a card goes into a private zone (where cards are not face up, such as your deck or hand), the game "forgets" that a card did anything. If Unown were to go into a private zone, Farewell Letter would reset. However, since Revive is moving Unown between two public zones, this doesn't happen.
soo.... what is the real answer?