I don't know *exactly* how it works, but apparently the difficulty (+1, +2 etc) determines which pieces are available to drop. I think gold jewelry only drops from vet +3. As for the rest, I think it's something like "Gloves and belts can drop +0" or such. (Gloves and belts just being an example of the system, like I mentioned, I don't know exactly what drops when)

You only get Perfected drops from the Z’Maja fight. Any mini bosses taken down before this fight will drop non-Perfected. In +0 you get 1 weapon, +1 adds 1 armor piece to this, +2 adds a purple jewelry piece. In +3 I believe you get 2 armor pieces, 1 gold jewelry, and 1 weapon, but I have not cleared +3 on vet to confirm.