A little while ago, I purchased this group of five plate number singles from a dealer, for no other reason than they amused me and the price was right. (There was one other one, still in the dealer's inventory, that I didn't go for because it was a duplicate.)

On another site, someone suggested that this might have been done by a collector who had seen the practice done for imperforate stamps. I don't have a better idea, and that sounds like a good story, but I would be most interested to hear if there are any other ideas.

