~~~ as Jay P. points out in the "What's worse" thread by Chuck Mades, below...

One example, and there have been many instances when a manufacturer may keep one piece of a run and cancel it by drilling, notching or shaving one corner of a plaque (there are other methods of cancellation) as they do with manufacturer salesmans' samples... and, should one of those chips/plaques surface years later, especially when the complete inventory has been destroyed, that one piece would certainly be a one-of-a-kind example.

Recently, some of those pieces (the one below is from 1969-71 and casino closed in '71) turned up on eBay Auctions that have never been seen before in either a manufacturer's catalog or anywhere else known by the hobby.