I've seen several Chipcos with an overstamp as you show, John. The ones I have are actually a re-identification of the the chip to use at another club. Have them remarked for Frontier in Calgary and Hilton in Puerto Rico. Apparently a way to make very inexpensive chips for a short term or NCV situation.

Below is a scan of a big baccarat chip from Desert Inn with such a cancel.

By the way, the overprints are very "permanent"; I've never found a way to remove them, only make them lighter.

DonL