Mike Irwin;
I also have a 38-200 / 5" / "V" -Series that isn't marked "U.S. Property" although it does have the "G.H.D." inspector's mark on the butt. There is no question that some guns got out of the factory without being stamped. The question is; was the mark overlooked during production or was it a deliberate omission? I think the answer is, "both." Like you, I have seen Victory Models that weren't marked either.
The now little known Defense Supplies Corporation (DSC) was created on August 29, 1940. This was a government agency that was to: ...stockpile strategic and critical materials other then rubber, ninerals and metals, and otherwise facilitate production and procurement of necessary materials. Among other things they purchased many thousands of small arms for defense plant guards, state and federal police, and other federal (non-military) and state personal. (Pate).
These were government orders, but not military orders.
Some 128,000 handguns were purchased by the DSC from S&W, Colt and H&R. (Pate)
They may also have been a cover for the OSS and other covert operations, and what they purchased wasn't necessarily marked according to military regulations, as this was a civilian agency(?) In wartime who knows. I would bet that at least some of those unmarked revolvers were sold on DSC contracts, but the only one who could find out is Roy Jinks at Smith & Wesson. He has the records.