I don’t think there’s 2 “clear” paths for every Exploration out or Modern in.I expect you to be proven wrong in this regard. Care for a bet for told-you-so bragging rights?
We now have all Antiquity civs announced and each and every of them have at least 2 clear options. Likewise, for every Exploration civs we can easily trace at least two predecessors and at least two successors. And for every Modern that we are confident to be in the game, we can trace at least two predecessors. So I'm pretty confident that it's indeed the rule and that the game is designed so that it was always possible not to have duplicates.
I'd go as far as to claim that every civ has exactly two options, but naturally, I'm less confident in this claim.
Songhai only showed Buganda as a path out and most of the paths people have guessed are not likely to be “clear”.
If they are trying to have civs each have 2 “clear” paths in then I think France may be the only Modern european civilization.