Stolen stuff wouldn't have been uniform. Besides, Poland was pretty much looted out by the Germans already. So it's more like the Soviets were finally winning enough that they could start specializing production a bit. (They lost a lot of industry early in the war, and after that a lot of workers, so what they had available was used only for the bare minimum - any variety would reduce production.) Possibly it could have been lend-lease from the allies, but that was mostly aircraft and trucks/engines IIRC. A fair amount of cotton, though, so it might be such deliveries that finally made their way to the front.