Video Game Release Dates: Demos, Open Beta, Early Access, Full Release

While much has been written about Release Dates for films & television, information on handling video game release dates is much harder to come by. When video games were released on cartridges, floppy disks, and compact discs, the release was easy to determine. However, as the distribution method has increasingly shifted to the downloadable format things get murkier. How should we handle a video game's release date regarding work-in-progress and partial releases?

It has become more common place for video game companies to make incomplete and unfinished versions of their game available as Demos (play a select level or a select amount of time - intended to build interest/hype) and Open-Beta Testing & Early Access (work-in-progress version - intended to get user feedback/find issues prior to wide release). Should these "releases" be treated as a valid release date for the full version of the game in the same way that film festivals are included in a film's release, or should they be viewed more akin to test audience viewing and sneak previews?