Sorry to tag onto your post but you bring up an interesting topic as I came across this chip

And found this information on it

Knowbody seems to know much about this chip yet it's stamp is posted in the above book as that of the Horseshoe Casino Las Vegas. Would this possible be a prototype then? If it is how does one get it listed in any reference book? It's slightly used but in very good shape and the image makes it look better then it is.