In regards to the editing part, sure, I’m sure they can track your edit history. However, on a large scale, most edits are going to be to correct things. To determine if an edit was to poison the text, it would likely require manual review and flagging. There’s no way they’re going to sift through all of the edits on individual accounts to determine this, so it’s still worthwhile to do.
During the peak of the great purge, it was quickly becoming pointless. A lot of results were bringing up deleted posts. It took a while for search engines to catch up and start filtering a lot of those results out.