Okay, I don't know what happened but i was playing on my Xbox and I was in my Vindel Hall and i put the nightingale hood on the manniquin, but quickly changed it to the dragonbone helmet. then I left. when i came back to Vindel Hall. I found a second Nightingale hood on the manniquin. at first I was like " [censored] yeah!" but now it won't stop spawning nightingale hoods. please help! I have about 200 nightingale hoods and I think I got enough. And that isn't even counting the ones I sold. Yikes.

It's a glitch wherein you can duplicate armor. Often times it does to you what it's doing and just keep replicating items.

place a full set of armor on the mannequin, but "quickly change" it to nothing and leave (NOT the house) the mannequin, then place the full (SAME) armor set on the mannequin and leave it on... try that?

I will try that. I get back to you on how it worked.
Oh and the dragonbone helmet, Nightingale armor, Ebony gaunlets and Ebony Boots look bad@$$ and makes you look like dark lord or something.