You're gonna be bothered by how cool I am.

Well, "the verbal sinking some of them say they need to believe it" is a moving target. The TLC/MN interview was perfectly clear; hence the many months it took to come up with the house-of-cards rationalizations that it somehow didn't say what it appears to. If they don't believe that, I don't think they'll believe most other "verbal sinkings" JKR might come up with, no matter what they say ahead of time.

There's probably is some way Jo could put it that they would be forced to believe - if she yelled in anger or spoke with excrutiating, lawyerly precision. But why would she ever do that? She's just enjoying talking to her readers about her books, not participating in the fannish inquisition. She has utterly no motivation I can think of to pedantically and overprecisely communicate something she thinks she's already made clear.