I think this quandary really is unknowable. It is clearly empirical that no matter how far the Endless Empire expands, there is more untamed wild lands yet to be settled, and that you can sail far far away beyond the reach of the Brazen Throne and find strange lands never before seen, either unsettled because of how environmentally dangerous the locale is, or mired in its own queer politics.
And so it might be elsewhere. Heck, you got the also currently unknowable question about whether other worlds exist in the Prime Material (clearly they do, Pathfinder becomes a Sci-Fi setting, and if we're going off old cosmology with only a hint of Pathfinder, there could be other fantasy settings out there).
That's all irrelevant as you said so long as you're not paying attention to them, and they never seem to have any real effect on what you're doing. Metaphysics can drive plot, too, like only the big ancient planar empires ever being relevant, if ever, on PM politics, despite the fact that there likely exists nations out in the planes with wealth and military force to dwarf a single continent (but no way to leverage it, unlike the Genies).