The fact that Reddit can still tell you that the user deleted their account is proof that not all of that user’s data in their systems are deleted. It may just be a flag in an account that marks them as “deleted”, and so whenever data about that account is being retrieved, their API server will look at that flag, and tell the recipient that the account is “deleted”. People in the software industry calls this “soft deletion”.
I learned in SQL class that you never ever hard delete data when there is any alternative. On Facebook and Twitter you get a whole month to change your mind before your account can't be recovered.
I've wondered about this quite a bit. If I were a fucking asshole like spez and wanted to defeat edit/delete scripts, I would set it so there's 2 entries, one is the original comment and a second column for an edited value. Everytime there's an edit update the 2nd one.
I had the idea to start all my comments with gibberish, and then edit with my actual comment, but that got a little tedious lol.
Depending on how their database schema’s designed, editing might not actually help. Some designs are made to track every change, so edits will just end up being a row in the database, and lookbacks can be super easy. For example, you might just have to ask the database to give you what a comment looked like at a given time.