William and Liza mention Sherlock Holmes and Dr. Watson - yet the film is set in 1875, 12 years before the publication of the first Holmes story, but this could be a joking reference to imply that Holmes and Watson are real people.
At the climax of the film Lady Charlotte wields a slide-action semiautomatic handgun - the first slide-action handgun of this type wasn't in production until 1898.