This is one of the hardest things for a writer to do. We write, much of it in our personal vernacular. We use certain words and phrases and usually don’t think about them twice.
But when we’re writing historical, it’s difficult to get everything right. NPR recently had a story in Fresh Aire, Historical Vocab: When We Get It Wrong, Does It Matter?
It’s an interesting problem that a lot of readers never consider. We writers try to get it right. I recall spending an inordinate amount of time trying to decide whether tarps would be called tarps in 1906 (They would not, it turns out. They were still called tarpaulins then….so that’s what I stuck in the text.)
Would someone have freaked out if I’d put ‘tarps’? Well, since I headed off that mistake at the pass, I won’t ever have to deal with it.
FWIW, there’s also one historical mistake that has been caught in the movie Lincoln so far, one that’s just a sign of laziness, since it should have been easy to find the information.