It's literally been proven that they do. A guy here on Lemmy was a very common poster on some tech support subreddit. He used one of those account scrubbers and deleted his account. He went back to look a few weeks later and all his comments were back.
I didn't delete my account but I used a script to edit all my messages to say that I have left because of the attack on 3rd party apps and when I check now they all still say that.
The point is doesn't matter what is visible, they could be storing all the comments edit history and simply not show it.
That only helps for a third party without access to reddit data , which they could have if reddit sells it to them, from scraping the page, yes in that case your comments cannot be used.
And they didn't bother to restore you because you probably weren't useful to make a community look attractive. He was so after he scrubbed his account, possibly with the exact same tool you did, they put everything back.
Yeah. At most they'd mark the comments as inactive, hide from the user accessible areas and maybe anonymize the user id. But they definitely have the username table and the data still in the system, 100%, just waiting for the right offer.
There are archives of all Reddit comments that are collected at the time of posting, all the deletion and scrubbing and whatnot people are doing months or years after the fact doesn't affect those.