Hi, Dave. I actually know all about those 20s. They were indeed used in the baccarat room, and are in fact not redeemable. I have a copy of the redemption notice from the R-J. In the '90's I had a friend at Harrahs who was a cage manager and she gave me access to the soon to be invalidated chips. I bought blues, reds, greens, blacks, a few of the 20s, and a still to this day unlisted $500. A couple of days later, they were all "worthless", but I have never seen them come out in any quantity since then. I have put a 20 on EBay a few times since then and always done well. I'm sure you will also.