Asklemmy

As a reader of historical fiction, I do prefer the background info to be factual. However, a good work of fiction, is, well...fiction. that being said one can't know all the details of characters personal lives and experiences - why it is ultimately fiction and those parts can't be factual no matter how hard one tried.

I think the important part is not to decieve the reader. I also enjoy pure fiction as long as I know.

That should be totally up to the writer

It should keep only some of the facts, the major, recognisable ones, but fictionalise all of the little details and incidents which we can no longer know happened anyway.

What was long time thought as "historical" facts often turned out to be nonsense and there is a lot of historical revisionism happening all the time.

I think if you write a historical fiction it is a moral obligation to add quite a bit of editorial context as a foreword or addendum to allow the reader to differentiate between unknowns, artistic freedom, historical interpretations and actual archeological evidence.

Edit: if you want to write "alternative history" fiction, it is probably best to also slightly alter names and geographies so that it is absolutely clear to the reader that this is a purely fictional account.

It should get the basic facts right at least, the details shouldn't matter too much (unless they're known & proven). Most importantly, it should be indicated which parts are purely fictitious

I find it a little bit disturbing that in Turtledove's books, he claims that green lizard aliens fought against both the Allies and Axis, when in fact no such aliens ever fought in WWII. He should have written those books more realistically.