There's no reason a universe can't spawn multiple sessions. Honestly, considering the number of void and dead sessions, it should be expected. We STILL don't know how the cherubs got where they did - Does someone end up Paradox cloning Lord English? That would explain their presence in the lab meteor, and it could be that there is some vitally important reason for paradox cloning the guy. And all the main characters are paradox clones - It's what the game system runs on. Paradox clones require ancestors, and I still suspect that Lord English is Caliborn and Calliopes ancestor.
With no lab meteor, it seems unlikely they exist pre-scratch, so there's only one version of them. But they still need an ancestor to be ectocloned from. So who is it?
Lord English is an adult cherub though. From what we've been told, properly becoming an adult cherub involves reconciling your "two halves", and Caliborn ruined that by killing her off. IF he wants to find her, I doubt he wants to double-kill her. I think it's more likely he wants to devour and subsume her so he can become a proper adult. (But I don't think it works that way, even if he suspects it to)
Lord English thinks (or so we have been led to believe), that Calliope is the key to his undoing. I am beginning to suspect that Caliborn might be as well. And that they will somehow become both an Anti-English, in addition to being LORD English. Especially with all the emphasis on ancestors lately, and the lack of any evidence seen of cherub-ancestors (which we know they need to have, as players of the game).... I think it's going to HAVE to play a big role. And it's getting to be a bit late to introduce new major players, but there's plenty of space left to shake out Lord English as something other than Caliborn.
Another question is, knowing as we do that each universe can spawn multiple incipispheres per scratch (humans + cherubs)... can each session be scratched multiple times? What happens if a Caliborn manages to scratch his session - is the human session erased too (unlikely)? Would the result even HAVE humans? (Since they didn't scratch, if their sessions stuck around I don't think it would, necessarily) These questions might not end up getting answered, but I think they are still pretty interesting. It might be that any given Universe gets "scratched" multiple times, with each iteration of the scratch being 'based' around a certain session, and the scratched version guaranteed a leadup to an ancestor-session in a more appropriate success-oriented world (for that particular group). If each scratch can produce multiple new sessions (each of which can scratch), well...
In that case, scratching as many times as possible would be an effective reproduction strategy.