So i've completed uplift reserve on legendary...again. No pop, no xp boost. However, like I mentioned above, I got it on keyes on CE. I'm curious, did they exclude ODST from this for this week?
Well this is just a "preview" of the challenges so it's tough to say. They weren't real clear on how this preview works really.
Thanks Tyler, With the launch of Halo 2 on PC, we are releasing an early version of our challenges feature
. This preview of the challenges feature is designed to meet one specific goal: granting players XP for completing campaign missions. Each week, the first campaign mission a player completes on each difficulty in each game in MCC will grant XP. Difficulties stack, so completing a mission on Normal will also complete that game’s Easy challenge and so on. Upon completing these challenges, a notification will appear, and the player will receive XP payouts tuned to the difficulty they played on. Each Wednesday at 10 AM, in conjunction with the weekly matchmaking update, players’ challenges will be refreshed. These challenges can be completed in campaign or campaign playlists
That is from the community update... So it seems like you should get xp from one mission on each game on each difficulty. So if you complete one mission on legendary in one game you should get the xp from each difficulty for that game but you won't get any more xp from that game and have to play another.