The missive is now useless. You should have chosen which bounty you wanted to complete as soon as the missive dropped. The old exotic bounties are no longer available as far as I can tell and the only way to get those weapons now is through the appropriate legacy engram when xur sells it.
English
-
Adding to this; if you'd had the actual quest before the update rolled it, you'd have been given the weapon without having to complete the quest line. Not to rub salt in the wound :/