Early 2015 Release Possible for Metal Gear Solid 5: The Phantom Pain
IGN reported that a Reddit user's copy of Metal Gear Solid 5: Ground Zeroes showed a special message when trying to register it. Registering Ground Zeroes resulted in screen saying that the player would receive downloadable content for Metal Gear Solid 5: The Phantom Pain in early 2015. This copy of Ground Zeroes was sold before its official March 18 release date.
In all likelihood, the DLC for The Phantom Pain will be ready upon its debut. This is due to the frequency in which top tier titles have had retailer-specific DLC and DLC that depended on previous incarnations of the series both ready on its launch date (such as the original Plasma Cutter DLC in Dead Space 2). This points towards The Phantom Pain's release coinciding with the availability of its Ground Zeroes' tie-in DLC.