I have a habit of providing edit comments when I edit my own posts. (I probably comment less than half the time when I edit other people's.) Because it's a habit, I do it even for edits within the 5 minute grace period of the original posting or a former edit.
I know that when I edit with a comment, then edit again, the same comment is shown to me (and I can change it if I want to.) My guess is that when that edit is saved within the grace period, my new comment overwrites the old one in the database.
But what about when I'm editing the original post? There's a place to type a comment, and I often do, but I can't imagine how anyone could ever see it and I confess to curiosity - is it in fact saved anywhere? Or just thrown on the floor when the code realizes I'm within the grace period?