The veteran page, link here, shows the back catalogue of Battlefield games (1942 or Heroes being two examples) that can be added to your personal library. When these games are added, they will give you a veteran status number, which is based on the number of Battlefield games you own minus one.

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For instance, if you own 3 previous Battlefield games, adding them on the veteran page, then your Battlefield Bad Company 2 veteran status would come out at the number 2.
To add a game, users will need to enter specific required information, dependent on which game they own and wish to add to the Battlefield veteran program site. For PC titles, a CD-Key needs to be inputted before the game is accepted into the system. Otherwise linking your Gamertag or PS3 account with the site will track which games you own on that console or system automatically. For Battlefield 2, users will be required to input their Gamespy username, as the online multiplayer facets of the game used Gamespy accounts.