If I had edited the comment you would see an "edited" tag on it. I'll do it on this one.

Edited to add this. Nevermind, there's no tag now. That's strange, I could swear that's a thing. Maybe I edited too early? Trying again now it's 18 minutes later. Still nothing, guess I've just imagined it?

I don't think it ever was a feature on HN. Although I've seen that on Lobsters and some other forums.