I have seen a similar thing - many years ago- but the explanation for that one is not pretty. We had a client with a ' problem ' who used to come to the Club every Friday and cash his unemployment cheque . He often lost almost everything within an hour , but always hung on to one 12 and 1/2 Pence chip , turning it over and over in his hands as if waiting for inspiration .
This could go on for hours . When he cashed it out , the cashier always washed it , giving a similar appearance to yours .
I doubt if this is what happened , but it's a possibility