I ran one of those greasemonkey scripts to (try to) delete my Facebook profile posts in mid–2016. Some months later I decided to just delete my account entirely. Many of the posts I thought I'd deleted were still in the account archive I downloaded before deleting my account (this was > 30 days after I'd thought I'd deleted them, but less than a year, so it may just be a data retention issue).

Yeah, but at least other people (third parties) are less likely to mine your data.

This would be a really good question to get a Congresscritter to ask a Facebook rep under oath. Maybe it doesn't matter and they'll lie. But I'd still like to get an answer: if a U.S. citizen deletes individual data, or the entire account, is the data retained in any sense? how does this differ for an E.U. citizen?

It still means Facebook can no longer legally use that data, at least in the EU.

If companies let laws get in the way of making money, there would be no need for enforcement bureaus.