The view gets populated when u do RMAN backup I belive. While backing up the RMAN checks the blocks it backs up and populates these views (v$backup_corruption,v$copy_corruption,v$database_block_corruption. So I belive it's not abour "after the last backup" but better to say "during the last RMAN back up.
That's my understanding but just to be precise, I am not completely sure about that. Maybe U can search the metalink for more precise info