I basically agree with you, Marian. I don't terribly mind anachronistic words because I frequently don't know precisely when a word came into general use. What I mind is anachronistic phrasing, as when contemporary idioms come out of 18th century mouths.
For me, it depends on how obviously out of place a word is. I'm sure I miss things, and I agree that it's probably impossible to know when every word came into use in modern English, unless one is an expert in that sort of thing. But some are bigger and more obvious bloopers than others. A word like adrenaline jumps out, because it is so clearly a modern, medical/physiological term and concept. Calling hair knotted at the back of the head a "bun" not so much, even if that is a relatively recent concept too (it's not like someone couldn't have called that hair style a "bun" earlier).
I also know writers and editors have to make choices based on comprehensibility to the average modern reader. Some words were in use in earlier centuries, but they had a different meaning. Nice is one such word. As I understand it, it originally meant foolish or vapid, though the transition to a more modern concept of the word had occurred by the time most historical romances take place. But using a word very differently than it is used today could cause confusion for a reader of a historical novel.
I do find it interesting how many romance novels are set in the late 1700s through the Victorian era. There are a smattering of titles taking place earlier and later, but those time periods seem most common. Perhaps it's because they are remote enough to be escapist and encapsulate a time with a slower pace of life yet close enough to have some creature comforts and relatability to the characters? There is an issue with HEA's set in the early 1900s also, since the spectre of The Great War is looming, and as a reader I would know a couple in their 20s who is happily wed in the first decade of the 20th century will be faced with horrific privation and the likely death or maiming of the MMC in about a decade.
I have read period dramas that are not romances (but with romantic elements) set in that time, however, because there was a lot of fascinating things going on in the first 2-3 decades of the 20th century. But period dramas tend to take place over longer time scales than romances, and if the characters end up in a good place, it's usually after a lot of dark grittiness one doesn't normally see in romances. Gay Courtier's
The Midwife and The
Midwife's Advice come to mind--it included Russian Pogroms, experience as immigrants, the takeover of women's health care by MDs, Socialist worker uprisings, the Bolshevik Revolution, and WWI and the Great Influenza, plus women's suffrage. The couple was together at the end of the book, but they went through a lot of hell to get there, and the books focused on a lot issues, with the relationship between the protagonist and her spouse just an aspect of it.
There is also that thing that for romances set in the UK, the MMC is nearly always titled or heir to a title. I read one recently where the MMC was an Earl's or something's younger son (he was a Vicar) and he had to deal with the possibility of losing his stipend/allowance from his controlling father, which put him in a situation that conflicted with his growing feelings for the FMC (who was the daughter of a Duke and therefore not an easy marriage prospect). But in general there seems to be a great fondness for Dukes, Earls, Barons etc. as MMCs with just the occasional country squire or younger noble son tossed in.
It is interesting, because by the 1800s, there were commoners who owned properties and businesses that were easily as wealthy (or wealthier) than most Nobles (some of whom were land rich and cash poor). I guess if one's audience likes reading about self-made fortunes, or MMCs who are wealthy industrialists, one's stories tend to be set in the US?
Though Courtney Milan has a few shorter works (novelette length) where the characters are commoners struggling to be in the middle class.