I'm assuming we won't be able to use ARR registration codes until the 27th or when the Mogstation launches. Once you register your actual copy of Final Fantasy XIV: A Realm Reborn Collector's Edition you will get access to your digital bonus items.

Some people already have their bonus items listed on their account because they were 1.0 Collector's Edition account holders which come with the same bonuses as the 2.0 Collector's Edition.