Jim Blanchard would know for sure.
He has the Burt records, they actually made the chips but their records would only show who the blanks and chips with inlays were shipped too. Distributors would have put all hot stamps on blank chips. Burt would not hot stamp chips. They felt hot stamps were too easily altered or counterfeited to put their name behind them.
BTW Burt made 90% of the clay chips in the world for a number of years.