Buying a series when I already have some seasons

Over the past few years, I have purchased individual seasons 1-4 of Game of Thrones when the iTunes Store put them on sale. The iTunes Store sells the entire series for $99. If I purchase the entire series, will I:

• Have the purchase price pro-rated for the amount already spent on the episodes in the entire series that I already own?
• Get charged the full $99, get duplicate episodes in my library for all of seasons 1-4, and waste the $$$ I already spent?
• Find something else happen that I'm not considering?