Continuity mistake: When John holds the match in the cave, the amount of match remaining varies between shots.
Continuity mistake: When Edgar Rice Burroughs receives the diary from John Carter's attorney on the table, he grabs the book and turns it around to have the book's spine on this left hand. However, when the attorney stands up and shakes Edgar's hand to say goodbye, the book appears with the spine to his right.
Factual error: John Carter, while gold prospecting in 1868, is arrested by members of the 7th Cavalry, with the intention of employing him to fight the Apache in the Arizona and New Mexico Territories. Unfortunately, in 1868, the 7th was otherwise employed in Kansas and Indian Territory forcing the Cheyenne, Kiowa, and Comanche tribes back on their reservations.
Continuity mistake: During the wedding between Dejah and Than when they are about to drink the water, Than's tattoo is on the right side of his face whereas in other scenes his tattoo is on his left. (01:46:25)
Factual error: Carter's war record says he won the Southern Cross of Honor during the American Civil War. While this medal was authorised, it was never actually awarded.
Suggested correction: John Carter isn't a real person either. This is science fiction, not a historical documentary.
It's still a valid point that he has a decoration that was never awarded. It's mostly science fiction, but the parts that take place in the real world are supposed to take place in the real world.
I think you're missing the point. The medal could have been awarded during that time, but no real person actually was awarded it. There's nothing preventing someone from being awarded it, and John Carter, as a fictional character, was awarded the medal. It would only be a mistake if they showed a real person who actually existed be awarded the medal or if the medal was never commissioned at that time.