Just try using the most recent launcher with all of the trainers and see if it works.
Didn't mean to imply trainer's MCC Launcher program not working; it is using the latest Halo 2 version for all 3 Halo games. Question is more related to each individual game recognizing the appropriate launcher so that it properly sync's with Steam in order to activate in-game achievements for each specific Halo game.
If the trainer's MCC Launcher is "universal", then my lack of achievement activation is an issue for Steam/343. Thank-you for your reply and your over the top gamer support.
Just try using the most recent launcher with all of the trainers and see if it works.
I tried this out and can confirm that Halo Reach MCC launcher cant be used with Halo CE /A and H2/A, while MCC launcher for Halo CE/A can be used for H2/A and vice versa.
When I tried to use Halo Reach MCC launcher, the trainer keep giving me errors whenever I tried to activate unlimited ammo and shield while when I use Halo CE/A MCC launcher, it works fine with H2/A.