Last night, I used Redact to delete all my comments, then altered the settings to make an exception for one and only one subreddit. To check if I even had comments left in that subreddit, I kept an eye on my comments through Infinity. At first the comments were being deleted one by one, then suddenly it showed a “No comments found” screen half-way through the deletion. So I looked through a post in that subreddit where I entered a discussion, and it turns out that my comments there were still up, despite my comments tab showing nothing. I then checked RiF and it didn’t show my comments through my profile. Today (after having deleted everything), I checked through my comments in my post in another subreddit, and it turns out they were still up, despite the fact that I didn’t make exceptions for it. Still found no comments through my profile.
Even overwriting might be getting undone, but that’s the best way to try it.