Wrong again~ Every seed planet that generates life can create a session, often several sessions. Near the beginning of the comic, Rose happened across that terminal monitoring the meteors. In one of the side monitors, it was monitoring an 8 planet session. We have not seen the session, it still exists.
The outer ring is infinite in size. LE could not reach all of them. Technically he is staying in a fairly local area based on that map. He's seeking Caliope and large congregations of ghosts. He has a general idea where they are since dream bubbles were formed by Feferi's request to the Horrorterrors as caretaker to the emissary of the Horrorterrors in her universe.
LE is not omnipresent. Nor is he omnipotent or omniscient. He can only be where he decides to go, if he were everywhere at once then he would have killed Caliope by now.
The other sessions exist and are completely unrelated to the ones we are watching.
Something tells me that no other sessions actually exist. We a) never saw any of them, not even in all of these dreambubbles, and b) the events in the current session set are already affecting all of sessions through the Outer Ring.
If there were any other sessions, we would see them trying to do something against the omnipresent threat that is Lord English, yes?
Yet we don't see that, ergo there are no other sessions, at least until the Lord English is vanquished.
That would make sense.
The trolls' version was found on a website or something. It's basically an unofficial leak.
The humans' versions were in Beta and Alpha, so it's like a test version. It seems odd to go from Beta to Alpha, but maybe it's because there were so many issues in the Beta session?
The troll version was found in ruins that Aradia was digging. And adapted to the current troll OS by Sollux.
Human version was distributed to many people by a company, hence multiple sessions and that 8 planet session on the monitor.