Other mistake: Inspector Lestrade of Scotland Yard says "I'm a close personal friend of Sherlock Holmes" and "he doesn't have an assistant." Both are incorrect. Doctor Watson is renowned for being Holmes' personal friend, assistant, and chronicler. Lestrade has always been a client or rival, never a personal friend. (00:58:06)
Suggested correction: In the novels he doesn't have a sister at all. Every version of Sherlock Holmes modifies the source material somewhat. Might be in this version Watson doesn't exist, or they've not started working together yet. Or indeed Lestrade is simply hyping himself up as a person friend when they're actually rivals.
Which novels? Sherlock novels or Enola novels? In both, Doctor Watson does exist. Yes, the film makers **could** have changed it in the film, but when such a thing happens, there is both the burden of establishing the deviation and justifying it. This film rides the Sherlock Holmes gremlin and uses it to attract viewers; plus, understanding parts of it needs a modicum of Sherlock Holmes preknowledge. As such, it is reasonable to expect it to take its burden of establishing and justifying deviations more seriously.