I have the similar problems except my issues are all my lists and contacts that were in my account from 2013 are not showing up and when I did a test by adding a contact that should have already been saved on one of those "missing" lists i get a message that the contact had already been added and it showed the date added (2013)
When I go to reports so see what campaigns had been emailed in 2013 and i click on the ones that were opened by the recipient there was a line through their email address as if it was possibly deleted?
Can you help!
I have taken a look at your account and can replicate the contacts on 2013 sent reporting campaigns are crossed out signifying they were deleted. Because the email addresses you tested with were able to be re-added easily it means they were not removed by the contacts unsubscribing. Have you previously deleted a large list of contacts? Does anyone else have access to this account?