Most of Russia doesn't realize that. In a previous life, I knew an old pilot who told me the grounds crew would have to paint American made planes into Russian markings and specifications.
Once the planes were produced, they would make a night flight out of the factory (California or Kansas) into some remote base in North Dakota where the markings were painted on under top secret conditions. Then there would be another night flight to Gander, Newfoundland, where CAF and RAF pilots would take over and ferry the planes to Murmansk after a refueling stop in Iceland. Again, these were night flights.
The Russians on the ground were sure these planes were coming from Russian factories.
Let's not overlook the strategery of the Nazi leadership. They fortunately made some real boneheaded calls.