This is no longer a CCG, having transitioned to Fantasy Flight Games' new Living Card Game (LCG) format. Excerpts from FFG's "LCG: A Player's Guide" (available here: http://www.agameofthrones.com/news-lcg-guide.html ):
"A Living Card Game (LCG) is a game that breaks away from the traditional Collectible Card Game (CCG) model by offering a new fixed card distribution method that still offers the same dynamic customizable, expanding, and constantly evolving game play that makes CCG's so much fun, but without the blind buy purchase model that has burned out so many players. The end result is an innovative mix that gives you the best of both worlds!
The first phase is the release of a LCG Core Set. Every LCG will have an amazing, high quality and widely available entry point packed with content, including high-quality game pieces and immersive game aides to enhance the game. Core Sets are completely self-contained, with multiple decks included, providing a great game experience right out of the box.
The Core Sets are followed by monthly installments of expansion packs, each a set of forty fixed cards, providing an ongoing and regular addition to the available card pool. These expansion packs add customization, variety, and an ongoing "story" to everyone's experience with the Core Game."
Starting with the Brotherhood Without Banners cycle, expansion packs come in sets of 60 fixed cards - 3 copies of 20 unique cards.
Starting in November they, Fantasy Flight, is going to reprint the King's Landing and Defenders of the North Packs to the new 60 card format.