Uncle Leo came from a situation of severe neglect, so that's how it started. Since coming to us in June or so of last year, he's regrown his green shoulders, blue collar and red pantaloons as well as about 50% of his chest feathers. He does still pluck a little out of nervous habit but is now easily redirected and far less emotionally stressed, so it's coming - we've even seen the odd feather under his wings and on his back. We're confident he will return to full feather but will likely always be prone to feather damaging behaviour if his environment isn't meeting his needs.
Casino plucks only during long periods of separation from me - once when we went on our honeymoon, once when he was injured and had to stay at the vet hospital, and again in February when we went on vacation. Once he gets started he ends up pulling out most of his contour feathers even if we return home. He then grows everything in normally at his next molt and leaves it alone unless/until the next time we go away.