The first commercially available automobile did not appear until 1888, and it looked very different from the cars seen in the movie. The particular Renault automobile owned by Rathbone was made around 1914.
The Statue of Liberty is shown surrounded by scaffolding as the ship leaves New York harbor. The statue was dedicated on July 4th, 1886. All exterior work on the statue requiring scaffolding was completed by that time, although the scene is set supposedly almost a year later.
The film was set in 1887, and ends with Roy O'Bannon talking about Hollywood and the new fascinating invention (Film) that is growing there. However, moving pictures weren't invented until 1894, in France, by the brothers Lumiére. And it took years before Hollywood came on the scene.
Roy screams at Lin that there is a "serial killer on the loose" when speaking about Jack the Ripper. Yet the term was not coined until the late seventies by FBI agent Robert Ressler or by Dr. Robert Keppel.
Ferdinand von Zeppelin did not seriously consider building his airship until 1890. Even though he had such plans in 1887, it is highly unlikely that anyone could invest in airships at that time as Roy did.
When Roy is sitting in the hotel talking with the mayor's daughters, we hear "Ain't misbehavin" being played by the pianist in the background. The song was written around 1927. The movie is set in 1887.
In the ceremony when someone is made a Knight or a Dame, the Monarch speaks that person's full name. Doyle was born Arthur Ignatius Conan Doyle. When Queen Victoria knights him, she doesn't say "Ignatius". Nor does she speak Wang's and O'Bannon's full names.
When Lord Rathbone revealed an automatic Gatling gun and said it was British ingenuity he was partially incorrect. The Gatling gun was a hand cranked weapon that was created by Richard Gatling, American, in 1861 and patented May of 1862. The first automatic, self-powered machine gun was invented by an American born Briton, Sir Hiram Maxim in 1884 and first displayed in 1885. The Maxim gun bared little resemblance to the Gatling gun. Automatic Gatling style guns did not come about until the 1940's.
Lord Rathbone would not have had to kill 10 members of the Royal family, but at least 20 to gain the throne: The Prince of Wales, his sons Albert Victor and George; Prince Arthur and his son Arthur Jr.; Prince Alfred and his son Alfred Jr.; Prince Leopold's son Prince Charles; and the Princes Christian Victor and Albert (nephews of the queen). Because British royal rule is not salic (meaning passed down along the male line, but rather, through immediate family), following the deaths of these people each of Queen Victoria's 'untitled' daughters would assume the throne in turn; Princess Louise, Princess Helena, and finally Princess Beatrice. Had these people been killed, the crown would have passed on to the eldest daughter of the Prince of Wales, Victoria, and, following her death, about 11 of her cousins in succession. Rathbone would actually have been 21st in line; not far from Roy's '20th in line' jibe.
During the fight in Rathbone's study one of the attackers is wearing chest armor. When the fight escalates near the ladder he is knocked over to the right of the ladder while the other attacker is stuck in the ladder. When he gets kicked by Chon he is on the left side of the ladder with no armor. In the next angle he is already standing and coming back to attack with his sword and armor.
When Chon, Roy, and Charlie are relaxing in the fancy house, Charlie pours Roy some brandy. When Charlie sets the brandy on the table, it is sloshing around in the bottle. After a brief cut to Chon then back to Roy, the brandy is motionless.
During the fight with Rathbone, Roy's knocked outside of the tower onto the hands of the clock. While the camera inside focuses on Chon and Rathbone the silhouette of Chon's arms can be seen, but not Roy's.
When Rathbone and Chon are sword fighting, Rathbone takes Chon's collar off with his sword and Chon reaches to his throat with his left hand. In the next shot his hand is in the air, and back to his throat in the shot after that.
Queen Victoria is shown as ambulatory. But, in fact, by the time the story takes place, she was wheelchair-bound. She was so overcome with grief by the death of her son Leopold in 1884, she had lost the use of her limbs.
The Boxer Rebellion occurred much later than the movie's time-line, but it is never claimed that the Boxers gang of London has any connection to that rebellion. Such connection also makes no sense, because the rebellion happened in China, not in England.