Thompson's were standard issue on tanks ... I believe each tank had two SMG's ... Here are tankers in a Stuart Light Tank on Bataan with their Thompson's (At least that is how the photo is identified)
From what I can find the picture is of Marines from company A of the 1st Marine Tank Battalion next to there M3 Stuart light tank near the river Tenaru on the Guadalcanal, yeah at the beginning of WW2 Thompson where shipped with each tank that is why there is so many Thompson parts in Russia because we sent them Sherman tanks and they didn't like/didn't have ammo for the Thompsons so they just put them in storage
While I do believe that during WWII the Russians received Thompsons with tanks and other "Lend-Lease" vehicles, I also believe they received them and .45 ammunition as aid.
Every weapon we provided would have been supplied with a "basic" load of ammo, otherwise the tanks would have not been of any use!
Years ago a large quantity of "repacked" .45 ammo came into the US from Russia.
Also, I recently read a de-classified article part of which covered the US Army evaluation of building the STEN gun in the USA.
The Russians were approached to see if they would accept STEN's as "lend lease" aid and their answer was no, keep sending Thompson's.
Not the answer you would expect from a country that just intended to store the guns away and not use them.
Its possible that whoever imported all the Thompson kits from Russia marketed them as never having been used.
I have had the same story with other former Communist stored material, only to find a mix of not used, used a little and refinished before storage (looks like new til you look closely)