In defence of Herlock Sholmes, I agree with him that the Diary, albeit a fake, if it is a fake, is not an amateurish fake. I mean, not quite in the style of a schoolboy faking a letter from his Mom that he's sick and can't go to school.
As to the claimed anachronisms, I'm not so sure. For how long must a word or phrase exist verbally before it's rendered into print? I haven't a clue. Yet there are words in Shakespeare which to our eyes and ears seem 'modern', but which may have been old and in general verbal use even in Shakespeare's time.
What kinda bothers me about the Diary is that its prose just seems awkward and even clumsy. OK, you might say that it reflects how Victorians spoke and wrote, but my grand-dad, who I remember very well, was Victorian, and he spoke and wrote much the same as I do. The Diary to me seems to be written in a kind of 'stage Victorian', for want of a better expression....I mean, did real Victorians converse in a style akin to the language in, for example, Oscar Wilde's plays? I doubt it.
We are suffering from a plethora of surmise, conjecture and hypothesis. - Sherlock Holmes, The Adventure Of Silver Blaze