I don't know much about how chips are manufactured, but it seems like (at least at one time) it was a pretty manually intensive process with setting the edge spots and inlays-- it's surprising that more errors didn't make it through.

Of course, even if they did make it through, you would need a good enough eye to catch them on the tables when they did, and then have the foresight to put it aside to so that future collectors could be jealous of them. No wonder they are so rare.

Thanks for posting

Brent J. Jensen
orbis non sufficit