On the subject of mistakes in King's fiction, I'm with you in terms of being able to empathize with the mathematician who winces at King's mistakes with prime numbers and such. For my part, I would never have known there was a mistake; I would not, at this moment, be able to definitively name you a prime number if my life depended on it. Not without using Google or guessing.
Most mistakes will fall into that category for me. A recent one that I remember is in "Mr. Mercedes," in which Janey discusses how her sister was going to take her to see a U2 concert when they were younger, but that an illness prevented them from going. She soon thereafter talks about how her sister got married in the late seventies, and that after that marriage the two of them drifted apart. Thing is, U2's first album didn't come out until 1980, so their first American shows wouldn't have been until at least then.
I know this because I'm a big U2 fan, so when I read this in the novel, it jumped out at me. Did it bother me? Not particularly. For one thing, I can always do what all hardcore King fans do when such anachronisms or gaffes pop up: I just rationalize that this is happening on another level of the Tower -- in this case, one where U2 evidently became a big deal several years earlier than they did on THIS level of the Tower.
If that fails, I'd just shrug and say that King isn't quite as big a U2 fan as I am, and that his editor(s) and various proofreaders aren't, either. So what? Big deal. I'm forgiving of errors like that, because, like, why wouldn't I be? I guess I ought to admit that it takes me out of the story briefly. But so do hungry cats, finished laundry, ringing telephones, the need to urinate, songs stuck in my head, and any other number of real-life distractions. Being taken out of the story is going to happen, always; if you can't find your way back to it pretty quickly, then it means either that you are a lousy reader or that you weren't enjoying the story much to begin with.
So my take on it is that people who get really wound up about errors like that in fiction are people who aren't reading for the same reasons that I read. But, of course, to each their own!