My limited knowledge on this tells me that the when the inserts plastic was being injected, the pathway to that lone diamond insert was blocked. Afterwards, when the red plastic is injected and molded around the inserts, the void was filled in with red plastic.

The injection molding process used by Bud Jones sometimes has this problem. It stands to reason that the blockage was NOT detected right away and that there may be more examples like this on the tables, or in collector hands. As for value, I would suspect that an error collector will pay at least $50 and perhaps upwards of $100 for that chip. If it was a Las Vegas chip, it would likely get more. If For Sale, I would recommend for maximum visability and optimum bidding.

Nice find, nice chip!

Jim