adaliabooks: Wait... ArmA is Operation Flashpoint?
Well, yes and no. Though they fill a similar niche, ArmA is actually a separate series of games, which Bohemia Interactive started because they lost the trademark on Operation Flashpoint. But while they didn't retain Operation Flashpoint's name, they did, however, still have the rigths to the actual game and two of its expansions. As a result, in order to be able to sell them, the game was renamed to 'ArmA Cold War Assault'.
In other words, it was retroactively turned into a part of the series, but it was originally a completely separate game.