Did he ever lose a fight?
I know he was never knocked down, but that doesn't mean he won every fight.
Was this ever made clear either way in the movie?
I got the impression he did lose fights, otherwise he would have been a much bigger success.
It was mentioned that he didn't have a great fighting record, but it would seem very unlikely that he would have had 64 fights if he had not won a fair number of them. You can't just keep constantly losing and still get fights.
There have been fighters like the character in the movie that could really "take a punch" that didn't have especially stellar boxing careers. Being able to take a punch is not something that I would want to be known for.