When does something become alternate history, again?

Via Bookslut, David Mitchell interviewed about his next novel. Note the disclaimer — “Such scrutiny freaks me out a little …. How the book ends up looking and how I might describe it now could be two very different beasties” — but it sounds promising. The short version is “Napoleonic-era saga set in Nagasaki.” The longer version:

I will say that my intention is to write a bicultural novel, where Japanese perspectives are given an equal weight to Dutch/European perspectives. It’s the most demanding thing I’ve ever tried to do. The research is a trackless swamp, and the book wishes to be written in ways that historical novels are not usually written in. It feels as if I am having to invent its “cinematography” as I go along.

[…]

You can only lay claim to a deep knowledge of a culture if you study it, live in it, get to know some of its people and learn its language, and most of us are too busy to do this more than once or twice a lifetime. So these “oven-ready perspectives” are what we fall back on, and they are probably better than nothing, provided that we don’t forget that they only scratch the surface. We mustn’t tell ourselves, “OK, I’ve got Japanese/UK/Any country culture sussed: I can stop trying to understand it now.” Opinions based on the perspectives you mention should be pending and conditional, in pencil and not ink.

And intriguingly, on the interrelationship of fiction and history:

If the question is asking, “Does fiction influence the perception of history?” then my answer is “Yes, and then some.” The skeleton of my knowledge of Classical Rome comes from Robert Graves; Victorian London, from Dickens; of Taisho and Showa Japan, from Tanizaki and Mishima and Akutagawa. Is there anything wrong with this, as long as writers write with integrity and readers remember they are reading fiction? Historians, too, are in the subjective narrative business, albeit narratives that try to capture the facts and facts only, those slippery eels. Witness the never-ending school history textbook debate between Japan and its neighbors: What are the facts? It depends on the teller.

Partly because of this, I decided very early on that my new novel must be set in a nearby parallel universe — one where global history is the same as ours, but the local history of Nagasaki is one of my own invention. This gives me the license I need to create my own cast, plot and locations, and frees me from having to spend the next two or three years as a researcher of vanished minutiae.

Without wanting to read too much into his words, I do find it interesting that he describes it as a parallel universe. It seems to me to imply, particularly when coming from an author with Mitchell’s demonstrated familiarity with genre tropes, something a bit more than the historical novel’s usual flexibility with regard to dates and events. At the same time, though, to what degree do historical novels owe fidelity to their period? I admit that one of the things that bothered me about Half of a Yellow Sun was that Adichie freely admits changing around the order of events in the Nigeria-Biafra war to improve the story, which felt at odds with her desire to bear witness to that history. And how much can you change a local history before the gap left by ignoring the knock-on effects that will inevitably have on the rest of the world starts to become obvious? (Linking to recent discussions on instant fanzine is left as an exercise for the reader.)