The pattern I've noticed.
The Dragon(skin,horn,leg,wing,etc.) armors come in 5 types. Matchless, Peerless, Heavy, Reinforced, and Worked, From best to worst.
For the most part the pattern is +or - 1 to the AC and stats for each level. It is wearable by chain and better classes and drops off dragons in Western Wastes.
The slots that I've seen armor for are Face, Wrist, Arm, Back, Feet Leg, Waist, Hand, Shoulders, and Chest