I dunno where exactly to post this, but i figured it's best to take it to the forums.
I don't want to delete what I think is the Mod's job on the main page for Dynamis, but I figured it -might- be of relative importance to say that you need the Key Items dropped from the respective ??? after killing the bosses in order to unlock the new zones.
It's been years, so I can't attest to it, but I'm pretty darn sure you have to have the key items, not necessarily defeat the boss (although, defeating the boss isclear).
Just figured it might be of assistance for some of those groups that decide "Hey, let's just kill the Jeuno Boss anywhere!" and promptly get raped/lagged out due to respawns and unable to touch the ???.