AFAIK it should trigger with the start of the final credits.
Did you try logging out, restarting the Xbox and logging in again, to see if the achievement list is just not being updated?

Did you get 'Kill With Power', if you didn't already have it from a previous tactician mode difficulty save? Completing an honour mode game should give 'Never Say Die', as well as 'Kill With Power' if it isn't unlocked.