I have several Hubs with inlays.
Mason did the HS ones if their plant after buying blanks from USPC and Burt. Burt or USPC made the inlayed ones.
There are some inlayed hubs IDed in the USPC records. Blanchard could have ID's on inlayed hubs made after the early 50's.

Herz does not have records on inlayed hubs. But he has found die tags on a few of them.
I have an inlayed Bi-plane hub that we found an exact copy of a HS with the same picture. It is from CO.