I’ve watched the entire nightfall series, I watched 5 times the first episode with it second stories 5 times too, and the reward of it and the others are not unlocked. Somebody knows how to fix it or 343i is going to let it continue? This is frustrating.
If you are having trouble unlocking nightfall and have watched all the clips, the best thing I can suggest is to try playing some H5 to try triggering something. If you still don’t see the armour you may need to accept that you won’t be able to get it through nightfall. The armour is in the req pool, meaning you will still get it at some point.