Factual error: Raoul is the Vicomte de Chagny and he gets called that throughout the movie, even during the auction (which shows he didn't change titles when his parents or his brother died, for example). Yet Christine's tombstone calls her a countess when it should have read viscountess - or, even better, vicomtesse.
Trivia: When Christine removes the Phantom's mask, he pushes her down on the floor. Right after he says 'Curse you,' the camera goes back to her: she is half laughing. (00:45:30)
Suggested correction: She's not laughing, it's shock and fear, she doesn't know how to react.
Other mistake: When the phantom sings behind Christine's mirror in her dressing room, she starts to walk towards it, entranced. It's obvious he is behind the mirror, and it's a one-way mirror. But, when she touches his hand, wouldn't the mirror have to be opened up? They act like she can just walk into the mirror. (00:30:55)
Suggested correction: When the Phantom begins singing behind the mirror and Christine approaches, it appears as if she walks through the mirror to the other side, then grabs the Phantom's hand. The hallway she is taken into is elaborate, with gold human arms holding candles. Later, when Meg looks for Christine in her room, she finds the mirror odd and slides it open to enter the secret hallway, finding it dark and rat-infested. This proves that what Christine saw was in her mind and that she imagined she walked through the mirror.
Suggested correction: When you watch "love never dies" he leaves her because the phantom won the bet, it's implied they got a "divorce" so she is still a countess.
But, in love never dies, it shows Christine dying in the year 1910, (when the whole thing was set) but on her tombstone, it shows that she died in 1913. Since Gustave is ten years old, this would make Christine in her late forties-early fifties when she had him, which is practically impossible. This is why I love LND's music, but the story is just too cheesy and inconsistent to the original for me. Since the original creator of the musical, Andrew Lloyd Webber, has chosen to call it a "stand-alone piece." and not a sequel, I would not use it as a reference for future endeavors with the trio.
Vicomtesse and Comtesse are two completely different titles. For Christine to become a Comtesse, Raoul would have had to become a Comte, but he didn't. He remained a Vicomte, therefore, Christine's tombstone should have read Vicomtesse de Chagny. It doesn't, so this mistake is valid.