R59 It would be a good idea to hire some uptight, language-aware people, for sure.
I've been an editor for almost 20 years and I'm sadly well acquainted with how little people even register the language they use. Most people are not even aware of cliched and hollow fad language like "it is what it is," "at the end of the day," etc. They just repeat it. I'm not surprised that writers don't consider what sorts of language may and may not have been used during past eras.
One thing that has annoyed me for many years is the change from "being missing" to "going missing." I first noticed this change in broadcast journalism within the past decade. Little Amber is not missing. She "went missing." My problem with that is that this usage is technically wrong in many cases: if a person was abducted, then they were, technically speaking, taken and they did not go of their own vision. However, they still *are missing.* Anyway, this has irked me enough to provoke me to ask many other people if it irks them, as well, and not a single person I have ever asked noticed this change. Not one. But if a TV show or movie were set in the 1980s, and a newscaster said that someone had "gone missing," it would really drive me nuts. It's just one of those things.
I think in writing, too, there's a balance of how much "periodness" to put into something. If you were to write a story that were loaded with era-defining slang to the extent people actually used it, then it would probably come across as parody. Or if you did that in the 1980s, and scripted dialogue with as many "like, like, likes" as people *actually* use (even now) in their day-to-day speech, then that would be really distracting and tiring to the reader or viewer. And if you were to create something more archaic than that, from the 1800s or the Renaissance era, then you'd really alienate viewers or readers and they'd be distracted from the story by the language.
So, for example, even though Game of Thrones was not actually set in the Medieval era on Earth, that really is the era from which the series was drawing. And the early seasons that were written well very effectively balanced archaic language and dialogue with contemporary language so that viewers could feel like they've been taken back in time, but not to the extent that we wouldn't understand what people were saying. The last couple of seasons totally failed in that regard and became far too contemporary, and viewers noticed and resented it because that took us out of the world. So it's a balance.
Still, when Mrs. Maisel says "back in the day" and Suzy tells her "I got your back," it makes me want to stop watching the series. It feels careless and inattentive instead of intentional.