Factual error: Otis elevator is called that because Elisha Otis invented the modern elevator in 1859, 17 years before the movie takes place. It had nothing to do with the Duke of Albany.
Continuity mistake: When Kate comes back home after the punctured dinner with J.J., her hair is freshly done. Even if she had ample chance to do this, it's out of the question that the rather messy style she had chosen for the dinner was not intentional on such an important occasion, and there was no reason to change this afterwards. (01:00:25)NancyFelix
Continuity mistake: Leopold tells Kate that by his 30th birthday he had "become a blemish on the family name", meaning he must be at least 30 in 1876, making his birth year at least 1846. When he goes forward in time to 2001, he is said to be at least 148 years old, making his birth year 1853 (2001-148) which would make him 23 years old. (01:11:45)unkajes
Continuity mistake: At the end when Kate arrives at the uncle's house, Otis says "what seems to be the problem?" The doorman looks up at Otis, but the very next shot is Kate and the doorman is looking at her. (01:51:50)