I have a "foolproof" way of getting rid of retained shed pieces; if you use this method before every shed, you probably will never encounter them again.
I transform my snake's entire cage during shed time. I start a day or two after the eyes go blue. I "up" the humidity to around 70-80 percent, by putting moist sphagnum moss all around the cage floor. I keep my several layers of newspaper in there too, moistening them as needed. I spray the inside walls of the cage with very warm water from a clean spray bottle. I keep the hides moist as well; I use modified tupperware containers, and I make sure that all have some moist sphagnum in there. I know that most people only provide one humid hdie at shed time, but my snakes never seemed to use it, and I was having some pathetic 5-piece-plus sheds. Since I switched to a "humid cage", I have had nothing but "one-piece, eyecap-intact" sheds; this is what has worked for me!