It also looks like packs are also discounted http://game.raceroom.com/store/packs/
I also got an email:
SUMMER SPECIAL PACK
The Summer Special Pack includes 30 of our most popular cars and 15 tracks, for a fixed price of 49.99 € available in the RaceRoomStore as a Redeem Code
But the question still remains are you credited with the content you have already that ins in a pack?