Your question about how one might be able to distinguish Burt plain mold chips from USPC plain mold chips is a good one.

A while ago, Richard Hanover taught me some techniques to do that. The Burt company only created chips (both plain mold and with edge mold designs) with 7/8 inch and 1 inch inlays. Most of the USPC chips from the 1930s and 1940s are 1 1/16 inch in size. Some USPC inlays are even 1 1/8 inch wide. The USPC Co. did, however, make some chips with 7/8 inch and 1 inch inlays, with 7/8 inch inlays being common on their chips in the 1920s.

Also the standard yellow, blue, and red colors of early Burt Co. chips from the 1940s and 1950s are slightly different from the standard yellow/blue/red that USPC used. The standard Burt from that period red is lighter than the standard USPC red, and the standard Burt blue is darker than the standard USPC Co. blue. I'm mainly talking about BPOE and roulette chips here. Also, by the 1960s the color thing becomes more complicated.