Each plan has a limit to the number of subscribers on it's lists. These subscribers are counted as the accumulated total of all the subscribers stored in all your lists.
As duplicates only exist across separate lists, they count towards total subscriber limit. They would be automatically removed from the same list.
All your unsubscribes do not count towards the subscriber limit on your plan. Any hard bounces and complaints are automatically marked as unsubscribed and so, are also not counted towards the limit on your plan.