Unless they've changed something since The Dark Below, the primaries were only available from Heroic Crota's End. Oversoul Edict could be obtained from the Abyss, Abyss Defiant from the Bridge, and both Fang of Ir Yut and Word of Crota were from Crota himself. On Normal mode, armor could be obtained from the Abyss, Bridge, and Crota while Special and Heavy weapons were only from Crota. The class item was obtainable from a simple chest in the Abyss at first, but was changed to Ir Yut, whose loot acted similarly to a chest and was only available once regardless of difficulty. Radiant Materials could drop from any encounter and dropped from all chests. Exotics were possible drops from Ir Yut and Crota.

Well like I said, I could be wrong. I don't ever remember getting them in the normal raid. The first time I got one was in the hard raid when a friend of ours was showing us how to run the lamps solo with a hunter, and then how to fly over the bridge with the sword. Both times, we got an Abyss Defiant and an Oversoul Edict.

Yeah, the drops there are the same in normal and Hard. You just can get more shards/energy. And you could get an additional chance at a drop like armor + weapon or weapon + shards. Or some combination like that. The end game, at Crota, is where the true differences in loot drops come into play from normal and hard. One example, you cannot attain Black Hammer on Hard Raid. That is only a Normal boss battle Crota weapon drop.

Yeah, Crota drops the Primaries on Hard, and the special/heavy in normal. I know that for a fact because I was trying to get a Song of Ir Yut and a Light of the Abyss to complete my collection prior to RoI launching (I knew I was going to delete Destiny and stop playing when RoI launched because I had no plans to buy it).

Lol, maybe I'm wrong. That does sound right but for some reason I swear the first weapons I got were the primaries Abyss and Oversoul. And, with not exactly having a lot of friends, I would try to solo parts of the normal raid. Until I eventually found groups.