Quote Originally Posted by Jandor View Post
All I can remember seeing of the 8UC is a few empty locations in a flashback or short story, can't remember which. Nothing of the wider universe/multiverse.
We don't see it, but we are told that their scientists have done their research and know that it is the First which was rejoined to their world, which is the Source, which is the only shard that other shards are rejoined to rather than being obliterated into pure aether.

If they have the technology to work that out, then they should also have the technology to notice that they aren't actually on the Source but a weird splintered version while the real Source is fine. That does not appear to be the case.

We have never at any point had the story suggest the possibility of shards being sundered by events other than the original Sundering, and the story has presented it as purely about diverging timelines. I don't see a good reason to reject the reason they gave us and invent one that relies on a different mechanism.