double and triple printing as well as inverted. There should not be any serious value attached to these stamps. I have them out of curiosity.
Printers waste generally refers to stamps that appear to be errors but are not. They are misprinted material either by accident or intention. They were supposed to be discarded but enters the philatelic market through carelessness or greed. They were originally imperforated sheets. The perforation were added later to make them look more philatelic.