John, many years ago Chipco gave (or sold) overstamped chips to oganizations (training schools I think) as a gesture of good will. The chips were errors or overruns that they didn't have any use for. If my memory hasn't failed me, after a few years of releasing these overstamped chips some enterprising individual(s) (I think they call them thieves) found a use for some of those chips by sandwiching them in stacks of like chips and cashing them in. You will note that only the obverse and reverse are overstamped, the edge is not. I don't know how extensive the ripoff was (I'm sure Chipco and the casinos involved don't care to discuss what happened and how deep the losses were.) I obtained many of those chips just as a novelty and have many high value early Chipco chips that I would not ordinarly have.
Today all Chipco "samples" have their "business card" printed on the reverse (and probably no edge markings). Now you have the rest of the story. Best regards, Chuck Tomarchio.