I don't know, maybe there aren't any Unertl experts out there.

Peter Senich doesn't have a lot of information about them in his "The Complete Book of US Sniping". He does say that 5-6,000 were produced by Unertl for the USMC. Since the scopes were stamped with a sequential SN, I would assume that you are correct, the higher SN scopes are less likely to have been issued than those with lower SN's. The Marines continued to use some Unertls through the Korean War, but they also used the mass produced 1903A4 with the Weaver 330 series scopes.

You would think that the War Dept would have kept better records of to whom & where scopes & rifles were issued, knowing that 70 years later collectors would want to know. But, if they did keep historical records, they have long since been discarded.

Neal