Okay, I’m not sure where it originated, but here’s a link to a relevant comment. I read it in a post about deleting Reddit comments when I first started exploring the fediverse, and I’m not sure I can find it but iirc, a Reddit admin confirmed that when you check your posts, it only shows the top 1000 and comments are only pushed off this list for “new” additions, and the list is not repopulated when you delete things. Therefore, if you delete all your comments, then check the list, it will show none (or if you delete 100 comments, it will show only 900, etc). Something about how these lists are populated in Reddit’s system. It is also relevant that some of the Reddit delete programs out there use this list and so will never delete all your comments.
Varyag