That's the only possibility. The odds that, in a pickup group, nobody knows the dungeon are extremely low, unless you are at the bleeding edge of the game (or during beta testing, and even then).
In EQ, I think the only dungeon where I found myself with a couple friends, and none of us knew anything was Befallen. After that, at least one of us had been there before in this or that group...
(and, of course, after dying once in Blackburrow, and needing 48h to find my corpse, I never ever entered a dungeon without having a printed map from EQ Atlas... strong death penalties mean you NEVER enter a dungeon unprepared)