Other mistake: Bruce Willis's character has a very clear scar on his forehead in some scenes (I think it's on the right as you look at him) - doesn't really fit the whole "unbreakable" theory. You'd think they could have put some makeup on it...
Character mistake: Various newspaper clippings are shown on the wall. There is one apparently in Italian saying "130 muore en aeroplano accidente." If this were Italian it would read: "130 muoiono in un incidente aereo." If instead it is Spanish it should read "130 mueren en accidente aereo." (01:40:00)
Other mistake: David is supposed to be immune to disease, which is why no one can ever remember him getting sick, but at a number of points in the movie the Chicken Pox scars on Bruce Willis's face are visible. If he was immune to disease, he should never have had Chicken Pox. I noticed this best in the scene where he asks his wife if she can remember him getting sick, look at his right temple.
Revealing mistake: When Bruce Willis bumps the guy in the stadium with the gun in his pants he has one of his "flashes" and the camera zooms in in slow motion to the side of his face. You can see that his ear is pierced. He must be "breakable" if he has a hole in him.