I think I would like it better if the special achievements said "you may claim this immediately...". Just because in IRL games that means that if you don't happen to notice e.g. that you've got three of each icon, then you're playing illegally; and then if someone else happens to claim Empire when you should have already had it, the game's a trainwreck. "You may" would make explicit that if you don't notice you qualify for an achievement, you're out of luck, but you don't have to cancel or backtrack the game.