Are you feeding live?
I feed live and I usually get a few less than I think I'll need as someone is always in shed, or will refuse, some will take 2 a few hours apart if given the chance. I hate holding the nasty critters in a critter cage for even a day.
I will discard, or save seperately a refusal from a snake in QT. I will throw a refusal rat from my main stock to a QT snake, but never the other way around.