Factual error: The film is set in 1884. The locomotive used in the scene on the platform is engine no. 2857, a GWR 2-8-0 that was built in 1903, 19 years after the film is set. (00:04:35)
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)
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)
Suggested correction: He suffered a serious injury, but didn't die right away. There's no indication death was instantaneous.
Every word of what you said is correct. And that's the mistake! Death must have been instantaneous... that is if there was any. A "head trauma", as medical doctors call it, does not have slow-timed effect. The effects range from dizziness to more severe ones, e.g. loss of consciousness, loss of memory, or death. All of them are instantaneous.
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: 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: Viscount Tewkesbury uses Marquess of Basilwether as a secondary title. However, marquess is two ranks above viscount in British nobility; a secondary title would only be of a lower rank, and the only rank lower than viscount is baron.