Do not make this article live. This is just for our team. this is how it works as of Feb 25 2020.
Inactive Subscribers are essentially deleted Subscribers. If someone is inactive and the account owner wants them to be active again, they can make them active by manually adding them from Subscribers > Add Subscribers. If you delete a List, it makes all people who are contained in only that list inactive.
Unlisted Subscribers are people who've been removed from all Lists but haven't been deleted. You could make some unlisted by removing them from all lists. For example, this person is opted in, but unlisted.