Two mistakes..
I cannot believe these two obvious mistakes were overlooked.
1. The "hit me in the face" scene was supposed to have taken place in 1941. But both Jake and Joey look well into their late 30's. In 1941, Jake was 20 and Joey was 16. It's highly doubtful a 16 year old would be a boxing trainer.
2. When Jake and Joey are sparring in the gym and Salvy and his goons show up, there's a picture on the wall of a boxer with an obvious late 70's hairstyle.
Extra mistake:
Okay this mistake isn't so obvious but throughout the movie, Jake is considerably taller than Joey. But in real life, they were about the same height..