It sounds like you are going for continuity errors, and this isn't one, it's more of a deliberate mistake. But it's one of the most egregious I know of, and it actually makes me angry.
In the movie "Cinderella Man", Russell Crowe's (Jim Braddock's) foe is Max Baer. In the movie, Baer is depicted as a fierce, scary, and cruel fighter and horrible person. He is depicted as being remorseless for having killed two men in the ring.
Baer was a vicious puncher, but that was not at all his personality or nature. He was basically known as a "clown prince" of boxing. One of the two men the movie claims he killed in the ring, Eernie Schaaf, actually fought four more times before dying after a bout with Primo Carnera. While boxing historians have speculated that the beating Baer gave him several fights prior could have contributed to his death, that's totally unproven and unfair to hang on him in the movie.
As for the first guy, Frankie Campbell, that actually did die after a bout with Baer, Baer was wracked with guilt and provided the family of the fallen fighter with money.
Many people say that Baer fought with a fair bit of ambivalence after the death that led to him clowning more than attacking in the Braddock fight and others. He lost four of his next six fights after killing that man in the ring before finally getting his mojo back.
He was also a great Jewish sports hero that inspired millions at a very important time, including when he destroyed Hiter favorite Max Schmeling in 1933 in front of 60k in Yankee Stadium, wearing a Star of David on his trunks. Years before Joe Louis destroyed Schmeling more famously.
In other words, that movie turned a fun, sensitive, heroic, and well-liked guy into an absurd Hollywood villain for no really good reason. It's totally unfair, as Baer was a real person, with his own story, not to mention living family members. I find it totally egregious and unforgivable.
And it's not like we know NOW that Baer was a good guy. We've always known him as a good guy, the movie literally changed everything we knew about Baer. If they were so insistent on having a fake villain, they should have changed the name to a fictional heavyweight, instead of besmirching a real person.
From a profile written decades before Cinderella Man:
"Max hated fighting," says Mary Ellen Baer, his widow. "How he ever hit anybody, I'll never know. He wouldn't even strike his own children. All he wanted to do was entertain people. I can't imagine a person as soft as he was becoming champion of the world. He was so kind. He had no mean streak at all."
"He was one lovable bastard," says Tom Gallery, who promoted some of Baer's fights in the Los Angeles Olympic in the early '30s. "He's the last person you'd ever expect to be a fighter. Why, he'd be clowning around 10 minutes before a fight. But, oh, what he could have been."
"It is incongruous that such a gentle, ingratiating man should have been a fighter," says Alan Ward, former sports editor of the Oakland Tribune, who was on the boxing beat at the start of Baer's career in the San Francisco Bay Area. "I remember when he was training for an important fight up at Frank Globin's resort at Lake Tahoe. My God, now that I think about it, it might even have been the early part of his training for Carnera. Anyway, he did about three weeks of pretty tough work. He had his brother Buddy with him and his trainer, Mike Cantwell. Max was actually working hard. This was for the championship, mind you. Then one night the phone in my room rang and it was Max. 'Let's go to Reno,' he says. I protested, but after all, it wasn't too far and I was a newspaperman, so I said O.K. Well, we hit some spots. Max wasn't much of a drinker, but he liked the atmosphere in the clubs. Word got out that he was in town, so he had an audience wherever he went. All night long he entertained, dancing and singing. At daybreak he was leading the band at one of the all-night places—I believe it might have been a brothel. All this while training for a big fight. When we got back to Globin's, there like the portrait of doom stood his trainer, Cantwell. Max went out and did his roadwork without saying a word."