Here in the West, in 2007, we played Interlude and a little bit Kamael (it launched in December 2007). Dual classes didn't exist. You had your main class, and if you completed the subclass quest (Toi Raid bosses, Baium Blood) you could add a subclass. If that subclass reached level 75 you could become noblesse and add a second subclass, and if that reached 75 you could add a third. You could switch between your main class and any of your subclasses by talking to the relevant Master in town. Main class and subclasses could go up to the level limit (78)
Dual class was added in Goddess of Destruction, in 2011, with awakening and the new level limit (99). Dual class was the only one of your subclasses that could level to 99. And that's when the button to switch to dual/any subclass on the fly was added on your character status screen.
The "original" lineage 2, meaning C1, had a level limit of 75 and no subclasses. Subclasses were added in C3