Not sure if this is common knowledge, but it was new to me! Early on in the game, I stored a bunch of green gear in my player vault with the intention of passing it on to a new character. I just went through my old items again and after withdrawing them, most of them had the "+" symbol next to them saying they had been upgraded (completely). I'm not entirely sure how it works, but I figured it would be good info to share! Anyone have a clue how it works?