Goatroped problem

My brother and I finished Halo CE on legendary under 3 hours in split-screen coop, but I unlocked the achievement and he did not. I noticed this for a lot of achievements that player one usually unlocks the achievement and player two does not. Later content updates have fixed this issue for the most part, but the harder/more complicated achievements still suffer this issue.

Is there anywhere he can check to see his progress toward the achievement or does he have to redo them on his own?

You can check the progress in the achievements app. Should show a progress bar. You can also go into your player progression under the menu button for that player and see all your achievement progress in game.

The problem is, the achievement menu and MCC menu do not track the speed run achievement progress, at least not for Halo CE.