It's no surprise I have a degree in history. I spent my college career researching details until I could go no further. A proper historian grinds and grinds because we certainly don't want someone saying we are wrong or we didn't find that one glaring detail which would change everything we presented. In academia, that's pretty important. In historical romance?
We try to be as accurate as we can. I've been known to spend days trying to figure out if the word "chandelier" was used in the 18th century. Or if someone living in London would have a water pump in the house or would they need to go to a public pump. As details go, these are pretty sniveling and really shows how a historian type can get bogged down. Most readers aren't going to know and even if they did, it isn't going to affect the story. My new rule of thumb is if I can't find the answer in five minutes, it probably doesn't matter. Unfortunately, I hold other authors to the same standard. If I can find the answer in five minutes, they should have too.
This is where I'm probably unfair. There are details which our society assumes are correct and no one would think to check it (except for me). For example let's take cotton fabric. When we think of cotton we think of cheap material. We think of those old time calicos or the denim jeans we wear. Our undergarments are made of cotton. So wouldn't it make sense that poor or lower class characters would wear cotton? Except that the cotton gin hadn't been invented until 1793. Previous to that, cleaning the cotton from its seeds was a difficult, laborious process there for the fabric was prohibitively expensive. Therefore it was a fabric for the rich.
So is this important? Does it impact a story? No, not really. Not many readers are going to make the connection. There are far worse mistakes to make. And there are some historical facts which can be used where a reader through their perceived sense of history are going to think are dead wrong. I once used a certain swear word in a WIP and got criticized because it was too jarring and certainly couldn't have been used at that time. Sorry folks, it wasn't a cuss word until later in the 19th century. You can find it in court records as a regular ol' descriptive word for intimate relations. Or having an unmarried woman use the title "Mrs." If my heroine is a housekeeper or a professional woman of some respect, she will be called Mrs. no matter her marital status. But most readers won't know that and I would have to spend precious words on an unnecessary infodump.
I think the problem is that worrying about the small stuff can bog down the writing or, and I've read it before, can make the author look like a show off. The amusing thing is, as curmudgeonly as I am about historical accuracy, one of my favorite historical romance authors from the '80's wouldn't have known an accurate historical detail if it bit them on the nose. However I was so engaged in the story and the characters, I had no problem ignoring it. And that's the crux. If the writing is good and entrances the reader, then the small details don't stand out so much. But as writers obsessed with history, where do you draw the line?