I think the researcher made a typo when he wrote 3,900 imported a month... Here is an email from Erik that I have saved, I have his email and # if anyone cares to verify.
"The marking on the right side of the receiver is our importer's mark. BATF required our name and city on every gun as a starting point for the tracing process. We used "Golden Sate Arms, Dist. Inc" "Manhattan Beach, Ca." in the early shipments and later they allowed us to abbreviate to "GSAD INC" Man. Bch Ca. So yours is an early gun.
We used to bring in a forty foot container of 1900 guns every month or so. We paid $125- each in China, paid 11% duty and sold then to distributor's for $299.00 each.
Erik J. Berry"