I belong to several writer's e-mail lists. One of them is a historical fiction list, although what I'm writing isn't exactly "historical fiction". Recently, a whole long series of posts have come up regarding what constitutes historical accuracy in fiction. It started because yours truly criticized the historical accuracy of some romance novels, or, more precisely, the careless or nonexistent research of some writers of historical romances. Some of the writers there write historical romances, and got a bit hot under the collar about some of the criticisms made. But then it broadened to discussions about how much historical accuracy is actually necessary in any type of historical fiction.
This is an interesting question. I, personally, have concluded that "it depends". I have read a number of books that were, on some level, "historically accurate", but simply not believable in one way or another. One example of this is Judith Tarr's Rite of Conquest, which is clearly a kind of "history/fantasy", but it just didn't "work", even as "counterfactual" or "alternate" history. While you don't expect "total accuracy" in a fantasy, this just, for me, stretched way beyond belief. And yet it got all the major historical events right.
On the other hand, there is the work of the author Judson Roberts, author of an ongoing series for young adults(and other interested readers), called The Strongbow Saga. In the very first book, Viking Warrior, there is a scene that strikes me as stemming from a very "modern" sensibility. The scene is where Halfdan, the young hero, is fleeing the enemies who killed his family, and encounters a wolf pack in the woods he's fleeing through. He thinks of fighting and killing them, but eventually "persuades" them to leave him, and the pack trots back into the forest. Afterwards, he takes this as a sign from the god Odin, and he prays to that deity and goes on his way.
What struck me as somewhat "odd" in this scene was, that it was possibly more likely that someone living in the so-called "Viking era", would have been more likely to try to kill the wolves. Certainly twenty, or thirty, or forty years ago, writers writing a scene like this, would have had the hero killing a few. But that was before more or less worldwide environmental consciousness set in, and many people nowadays all but worship wolves. Even if they don't, wolves are considered to be very much part of the environments they exist in, and most people think they should be left alone for the most part. And this is where I think Roberts' "modern sensibility" kicks in. I don't think the man is particularly the type that tries to be "politically correct", but he might have thought twice about having a heroic battle with a wolf pack, when they have generally been persecuted most places, and still ar, in some places, and are decidedly endangered, in some other places. Still, that scene didn't jar, because the hero decided it was a sign from Odin, which some Viking era person might well have thought. In other words, it doesn't really stretch the credibility of the story too much.
Of course, if you're writing biographical fiction about real people, as Elizabeth Chadwick, whose blog Living the History, does, a great deal of attention to detail about the events of the times, and about daily lives, etc., is much more necessary. I doubt if I could write biographical fiction, even with a "good story", because I think I would get bored dealing only with "the known", so it's probably a matter of temperament, too. I, personally, like some invention and "twists" on things, which, for me, necessitates creating fictional characters, as I am doing with my Invaders trilogy(although one major character was a real person about whom not much is really known). But everyone is different, and every writer approaches what they do, somewhat differently.
Which brings me to anaother point. Some people object to anything other than what they conceive to be "total accuracy". This means, for them, not allowing their characters to do certain things that are common in romance novels(such as having female characters going off alone, or running away to be female pirates, or something like that). But still another writer pointed out that there were women(and men) who did things they were not "supposed" to be doing, for their time, or thought in ways they were not "supposed" to think, for their time. This author pointed out several historical examples of this. So again, this suggests to me that "accuracy" in a historical setting can be quite a tricky path to follow.
As I said, I think how close to "accurate" you must be if you are writing fiction in a historical setting, depends on what you are writing about, what research material is available to you, and even the genre you are writing in. "Straight historical fiction" is probably going to be a genre demanding more attention to historical detail, than a romance novel, which can use some historical events or other, as a background to the growth of a particular relationship. Athough even here, I think the author of a historical romance should strive to get at least basic details right.
What I'm doing is a blend of fact and fiction, and part of it derives from what I know(in some ways, I don't think I know all that much, and am still learning)of ancient, "archaic" humans and their capabilities and lifestyles. I have "blended" this knowledge into a medieval setting, which has a number of historical characters, and it is here that I want to get the details and historical events as "right" as possible. Even here, I have to "fudge" a bit, I think, because there's not all that much information availabe about some of the "real" characters, and only the bare outlines are know about some of the events I'm writing about. So I feel that in some areas, I have to "fly blind". But I don't pretend that I can say "Oh, who cares? It's just fiction", either. I think I owe it to my readers to get at least a "flavor" of the times I'm writing about. If I can do that, and perhaps inspire someone to find out more for themselves --- which is something I've often done when I've read a piece of historical fiction --- then I will consider that I have accomplished something worthwhile. And that, perhaps, is the best thing a writer of any type of fiction, even nonhistorical fiction, can accomplish.