Factual error: Towards the end of the song "Out There" Quasimodo climbs onto the large spire on the roof. That spire was added in the 19th century and thus didn't exist when the movie was set.
Factual error: During the riots and the start of the film a model of armoured car and grenade launcher are seen, which were not manufactured until the 1970's.
Factual error: In the scene with the brandy at the beginning of the voyage, Long John Silver says that the brandy was laid down by the brothers of Buckfast Abbey, vintage 1737. The monasteries were closed in England by Henry VIII in 1538-1539. Buckfast Abbey itself was surrendered to the king on Feb. 25, 1539, and soon demolished. It did not reopen until 1882.