Factual error: The old percussion double barrel shotgun is firing modern shotgun shells, which would never work or fit in that gun, and furthermore are also made of plastic, wrong for the era.
Factual error: At the end of the movie Enola rides a bike on the right side of the street. The shot widens and two horse-drawn buses come into view, also on the right side of the road. The movie is set in exactly 1884 (votation). It became mandatory to drive on the left side of roads in England in 1835 (Highway Act). (01:56:33)
Factual error: Linthorn meets his end when Enola knocks him off his feet. He hits his temple against a heavy and sharp furniture protrusion. Death must have been instantaneous, but instead, he lives to speak a few words. (01:39:18 - 01:39:55)
Factual error: Mrs. Harrison travels to a random, remote country mansion (kilometers away from any civilization), meets a woman who is not her pupil, forcibly takes her measurements, insults her, and slaps her! Nobody in the right mind would do that because they know they would be murdered, harmed, or handed over to the police for trespassing, assault, and battery. (Such outcomes are recurrently portrayed in Sherlock Holmes stories.) Schoolmistresses did use corporal punishment but only on their pupils and within the bounds of school, where they have relative safety. To make matter worse, Mycroft warns Mrs. Harrison in advance. He describes Enola as "unbroken", "a wild and dangerous woman", "a wild child." (Indeed she is; she beats people during the rest of the film. How did Mrs. Harrison escape unscathed?). (00:11:43 - 00:13:46)