Hi Bob,

"I get the idea that it was made as a prototype, but when looking closer it seems to have wear on some of the edges and some dirt. Could it have been made as a prototype and then (either by the casino or the manufacturer) mixed in with the regular chips?"

Could the chip have been a prototype and found it's way to be used on the tables? Sure. Either way, it's probably(99.9%) a one of a kind chip in the collectors hands. There might be others in the vault that most likely will never see the light of day.