I think this is the right forum section for this.
So today I wanted to see if playing the campaign playlists would give you credit for the Legend achievement.
Before I tried it out, I had beat the first two levels of Halo: CE on Legendary, so my Legend count was 2.
I chose to try my theory out with Halo 3 and I beat the first level. I am speaking of the real level, not Arrival, however they both were completed on Legendary according to my missions menu.
I checked and my Legend count was 3. Sweet.
So I went into the Halo CE playlist and played the first 3 levels on Legendary. The odd thing was though that my Truth and Reconciliation achievement did not pop for a few minutes (I hadn’t beat the level yet). This worried me and peaked my interest so I checked my Legend achievement count and it is still at 3.
To summarize, I have beat the following levels on Legendary and my game shows me it has already been completed on the Legendary difficulty:
Halo CE - Pillar of Autumn, Halo, Truth and Reconciliation
Halo 3 - Sierra 117, (I don’t think Arrival counts towards the achievement)
This is a total of 4 levels completed but my Legend count is 3.
The point is, this greatly worries me that what if I won’t be able to get the Legend achievement and I’ll be stuck at 39/40. I’m worried Truth and Reconciliation won’t be counted for some reason, and perhaps it can’t be counted because in my missions menu it is already marked as completed on Legendary, and yet I don’t think it’s accounted for in the Legend achievement counter.
Edit: I turned my game on and checked my Legend progress again and it now reads 4/40. This is great news and I hope it doesn’t happen again.