This may be subjective on my part (hence the question) but every time I read a comment or interview by Rowling I get the impression she’s building on the idea of “I had it all planned out from the beginning” (warning, TV Tropes link) and back justifies a lot of stuff in very weird ways.
Other than the old “being bad at math”acknowledging being bad at math, has she ever acknowledged openly something on the lines of “yeah, when I wrote that part this complete other side of the plot hadn’t been fully defined so I had to adjust a bit to make it work”? Or, “yeah that part about Slytherin being mostly bad became a pain later on when the series evolved.”
Note: this is not meant as a rant against her. 99% of the quotes I see for Rowling are on this site. As such it makes sense my perception is all are justifications as they are brought up to precisely answer a question on this site. I’m curious if she’s normally open about her work or not.