I haven't had an 'oh no' moment in my current version of JTA.
But i had a big one in the first version I wrote.
I always like first person perspective as i tend to find more intimate to the characters... In one of the old version's chapter I actually started the chapter with one character narrating and ended with another one.
When a chapter is too big (mine usually go over the 10pages mark) i tend to take a break in writing, It seems on that particular chapter I took a break when i was writing a sentence for a character that wasn't the narrator, and when I came back i just continued on as if they were.
Luckly i never published it, I passed it onto my mate for test reading and he pointed it out to me xD
I do have a lot of 'oh actually' moments, again, due to the first person perspective sometime i'll begin writing a chapter in the perspective of one character only to find out it would have made it more interesting to have it done from another character's perspective.
That has happened to the current version of my story, but normally i don't mind those, it's just a natural realization and it makes sense to switch, even if I do have to rewrite over 10 pages sometimes, it's for the sake of giving the reader the most fun and engaging experience.