My main point was that "what's inside Jim's head doesn't matter until it's on the page" is a valid interpretive model. I just disagree with that model. Mostly.
What's in Jim's head matters more now that it would if he wasn't writing anymore DF books because it is likely to inform where he's going.
Well, here's the thing: Jim has his own "headcanon" of stuff that's going on, simultaneously with the DF stories he writes. He narrates the Harry-POV account of events (or sometimes other narrators, in the shorts), cackling insanely as he DOESN'T write down the narrations of the Evil Genius'es who are operating undetected, behind Harry's back and right under Harry's nose.
But that stuff really DOESN'T matter to those already-written books. The books stand as they are (until/unless Jim goes back to do a re-write / re-release, to eliminate Early Installment Wierdness, to alter some clue-drops to more accurately reflect what Harry would have known, etc etc etc); they are bound volumes, with no headcanon enclosed. I DO admit that it's GOING to matter in future books (although by that time, "today's" Jim-Headcanon may have evolved into something very different!).
Except it DOES matter, right now... to a few obsessive fans who analyze and dissect and WAG about it, and write
way too much,
way too often, in dingy little forums (with apologies to @Griffyn612) deep in the bowels of the Internet.
One of our chief problems, frankly, is Jim: we're trying to dissect Jim's headcanon. It's like the game
Battleship, where we make our guesses and WAGs, and call them out on AMA's and Con events and bookstore events &c. And sometimes Jim answers, and sometimes he doesn't, and sometimes he overtly lies, and sometimes his headcanon actually changes: he moves his ships around on the board!!!
... For example, I don't put a lot of faith in pronouncements from J.K. Rowling that "that character was always [insert most recent political fetish] even though I didn't put a single thing in the books to indicate that.
Speaking as someone who read the books as they came out (well... I was a year late to begin; but otherwise ...), and someone who's a straight male raised before the days when very many folks accepted gays: I found the "Dumbledore is gay, and he & Grindelwald were a couple" to be 100% on-point; it settled the character, resolving issues I had found odd and/or incongruous. Some of the other pronouncements from Rowling... yeahNO, not really feelin' it, very WTFish!
I was shocked that "Dumbledore is gay" caused so much uproar, because I found it such a "well,
duh, of course he is!" element.