The USMC markings are found on every USMC contract Unertl. I don't know of any large scope order by the War Dept that was submitted without evaluation of the commercial version of the scope to see if it was satisfactory. (Weaver 330 series, Lyman Alaskan, but probably not the M84)
Add in where it was found, I would think that yours is an evaluation scope. (Unertl wouldn't have asked for it's return.) But, you aren't going to find anything in the way of proof that it is the real thing, & probably nothing on exact serial numbers of contract scopes actually issued. It was just inconsiderate of the soldiers working in supply not to keep detailed records; they should have known that, 75 years later, inquiring minds would want to know.
Neal