Watched 1917 last night. Enjoyed it, apart from the shot where a British soldier gives the middle finger to the lorry driver, rather than flicking the Vs. As this has only been imported to the UK from Europe/USA in the last few years, this would not have happened and would not be a thing. Also, the following bit of dialogue would also not have happened:
"We've got the Bosch on the run."
"No, we don't."
The response would have been; "No, we haven't." The use of 'don't' instead of 'haven't' is another Americanism that has only just hit these shores in the last few years. It would have not been in use in 1917.
What surprises me is, so much work is done in ensuring that all the sets, uniforms, vehicles etc are factually correct, but no one checks the use of language or mannerisms etc. This might not have registered with some people, but it leapt out at me in the same way that seeing an Austin Allegro in a 1960s film would.