I have some chips (Crown Casino out of New Orleans-never opened) that were cancelled, and somebody washed the gold stamp off, but the plastic is still there.

I suspect it was done to make the chip more valuable. They failed, I bought it out of a dollar bin ($500 chip), I actually was concerned that I had accidentally bought a valuable chip, but that was when it was explained to me about the stamp.

Thge person I bought it from is very reputable, and that is why it was in his junk bin.