The "Game Details" panel for http://www.giantbomb.com/starcraft-ii-heart-of-the-swarm/3030-24078/ have the information "First release date: March 12, 2013". However, http://www.giantbomb.com/api/game/3030-24078/?api_key=[insert your key] have no data on "original_release_date".
Investigating further in specific releases, such as http://www.giantbomb.com/starcraft-ii-heart-of-the-swarm/3030-24078/releases/#toc-release-125223 have the information that "Release date: March 12, 2013". But once again, http://www.giantbomb.com/api/release/3050-125223/?api_key=[insert your key] have no data for "release_date".
The release date data in the API is missing. But visible on your pages.