Yes, yes, but there's always tomorrow -and as my trade is translation, I always prefer originals. Screw the competition! Wait, that's a civ phrase, but addled gamers might occasionally have a point.
What if the tech is obtained with the Great Library or another such wonder?No, it doesn't. Only if in the meantime you obtain a new tech (by research or by trade), as already pointed out by justanick. The tech doesn't need to have anything to do with the units. Just the fact that a new tech was aquired seems to cause the game to trigger an algorithm that goes through all city buildlists and checks whether all units currently under production are still "up-to-date".