I always return the extra material from the backing just for the reason you stated. Many customers want to use the pieces for the binding. Once in a while a stray piece will escape, but not often. I would email the long armer and tell her that you'd like to use the backing pieces for the binding, but the piece that was returned isn't big enough. Ask her if she can locate the missing pieces. It doesn't mean she kept them on purpose, but she'll probably be more careful in the future.
Peggles