They store the current edit and one previous version back, and deletion does not count as an edit as it only hides the latest version from showing on the front end and through the api.
This was found out by people trying to edit and delete comments in mass during the api exodus.
So you’d want to edit the comment to garbage twice before deleting it, and hope they aren’t willing to restore shit from deeper backups they surely have for system safety (speaking as a systems engineer) that they haven’t pulled from yet.