Answer:
A person who unsubscribed or whose email address would be considered invalid following a hardbounce or 5 softbounces will not be recreated in the list during an import.
Also, the contacts already existing on the list will not be created a second time.
Finally, it is important to make sure that you have added a column populated with your unique identifier (“original ID”) in your file. You must identify it in the mapping at the time of import.