They would not have come from Burt!!!
Alonzo Burt started Portland Billiard Ball Co in 1912 - 1st chips made in late 1920's

USPC could have been the only Co making clay chips that early.
TR King was selling plain mold and Lcrowns made at USPC pre 1936 but I don't know when they went into business. No TR King records exist pre 1936.
HH had a good article on TRK a few issues ago in club magazine. Take a look at it.