For historical fiction - I think sometimes people (I'm not referring to anyone in this thread) need to remember that it is exactly that - fiction.
The great Edna Ferber made reference to that in the preface to one of her books - I think it was Cimmaron. She acknowledged that a couple of the dates she assigned to real events were in fact a year or two off - but she had to do it that way, in order to make the rest of the story fit. She did have a rather creative term for nitpickers who would constantly let her know how "wrong" she was (I gather people did this by snail-mail in the 1920s and 30s) - unfortunately I lent out my copy so I don't recall exactly what it was.
There's a difference between bending the facts a wee bit and not bothering to do your research at all. A modern author cannot assume that if she can't find it in a 2-minute search of Wikipedia, the answer isn't there at all, so she can make up whatever nonsense she likes. You can also get nailed by those things that "everybody knows"; let's take on two of the most common: 1) Medieval swords weighed about 20-25 pounds, and 2) armor was so heavy that knights had to be winched onto their horses.
Typical swords (of which there are a surprising number extant both medieval, Roman, and even older) weigh between 2 1/2 and 3 pounds, just over a kilo for the metric folk. Even the really big flamberges and other two-handed broadswords weigh less than 10 pounds. One of our SCA members had a replica flamberge that we would allow people to heft at demos; they were surprised to find out that its actual weight was 7 1/2 pounds, less than a gallon of milk, as their guesses were always in the 20 pound range.
As for being winched onto one's horse...far from it. A medieval knight was supposed to be able to jump
onto his horse's back from the ground, without recourse to stirrups. He could run, jump, and even turn somersaults while wearing full armor. (Swimming, however, wasn't a very good idea.) Depending on the type of armor, the exact period, and the place, armor weighed from 30-90 pounds.
The heavier end of this range represented late-period jousting armor, a different beast entirely than combat armor. Still, even that weight didn't require winches -- that appears to have been created by Mark Twain for A Connecticut Yankee in King Arthur's Court.