I’m not sure if it’s a coincidence, but I raised a case with the ICO in the UK, and today they got back to me asking for all my communication with Reddit. Also today - after a month of silence - Reddit also emailed me with this
If you’re in the UK and had been affected by posts being restored, I’d recommend contacting the ICO. It takes less than 5 minutes
That's pretty dubious, otherwise why would I get all these replies from 3-7 years ago? Not new replies on dead threads, but the replies were posted that long ago, and I'm being notified about them now as "new" comments. Seems a lot like deleted posts coming back.
This is why Power Delete Suite edits the comment before deleting it. If Reddit is keeping a record of deleted posts and comments, then theoretically they'd only be left with a bunch of comments that say nothing. But I'm pretty sure that if they're keeping deleted comments, then they're also keeping edit histories.
I imagine they have full offsite backups they can pull data from. That's why we have documentary shows like Mr. Robot, never forget 5/9!