You just can't have more than 2 in a farming instance. (And only 1 in certain events/TW)
Probably rule wasn't clear enough. You can have unlimited amount of accounts in instance, but you cannot have more than 2 in farming spot (on the world map). That rule has been corrected to avoid confusion.
It was made so people won't abuse farming areas on the world map and take best places with their 2341233 alts, make lag and so on...