Well after the last fix, I have read, and experienced that you can now only retrofit "Player" created items with existing stats.
A) you loose the mods that are currently on the item and are left only with the item (armor, clothing), so unless you have a better mod to put on, you may want to simple re the piece and use the parts as scrap.
B)My experience has also been that retrofitting is a waste, unless armor has high protection on it and stats, cuz then you can remove the stat and re-fit it with a better stat.