The serial number of the firearm I am looking into is 814608, 5 inch barrel, 38 S&W.

Pate on page 118 lists serial number 817012 shipping on 8/26/1941 and being unmarked.

The letter is for serial number 702070, which I know isn’t close to either of the other ones, but says it shipped 9/21/1941.

Like you said, these travelled all over the place, so I know there will probably be never be a definitive answer to the history. The letter stood out to me more because it was something “in writing”. I have been tryin to note things like that and maybe some day a date, serial number, or location will tie in with something else.