If a chip is "unknown", put it in every guide stating that. You could have a separate section in each guide listing chips as to being "unknown" (showing images of the chips). Also, state that more research is needed to properly indentify the chip. I don't think a separate guide should be generated just for unknown chips - it probably wouldn't sell very much.

"If a collector has a reason to believe that a chip may have been used in a particular casino in a particular location, but doesn't have proof, I see nothing wrong with "attributed to" until its actual use has either been proved or disproved."

The collector's belief really doesn't matter in what an author believes or decides to label something as. The "attributed to" is just an assumption or speculation, not factual or proven. The author(s) of guides are stating to the person who reads or purchases his/her guide that we have no proof that said chip belongs to this casino, but we assume it does. Why not just tell everyone who uses this or that guide that this particular chip remains "unknown" at this time and further research is needed to authenticate or prove it's origin, manufacturer, whether or not it was actually used, what casino it was used in, etc.?!

Regards,
Thomas (R-7788)