I have Dragonscale armor on that gives me a 745 Armor Rating... so I'm a bit confused.

I believe the armor cap is 576.
Anything above that does not help you in anyway.
The game is still showing your overall armor rating at 745 but you aren't getting past the armor cap.

Alright. I just decided to make this armor since my Nightingale only goes to 467... it's amazing looking armor, it just isn't the best to me.