USPC made all of Mason's chips prior to the Burt Co buyout of USPC molds. If I remember right it was 1947.
There are hubs in the USPC records on the MOGH site.

The braces mold is not in the Mason chip records going back to the 1920's.
I don't think Mason ever used it.

USPC may have made it for someone.

There was only 2 companies actually making clay chips in those days after 1947 buyout.
USPC stopped in 1947.
TK King
Burt. Braces are not in any of the Burt records.

Are you sure your Braces is clay with no injection mark on it?