Any insight into how we should?Not necessarily, but arbitrarily splitting it in this fashion isn't a clear improvement.
I would really like to insist that whichever way we use should preserve the order of the choice adventures (i.e. avoiding "putting all choice adventures related to the elemental charters in this file, putting all choice adventures related to dreadsylvania in that one").
Doing so allows us to find "missing" choice adventures more easily, as well as duplicates (though there's the test for that one).
While doing the whole refactor on my end, using this format did in fact allow me to find a number of missing choice adventures (like one of the ChibiBuddy(tm) adventures), by noticing a gap in the choice adventures, what is before and around it, and digging further. I'd submit them, but at that point, my version is so different from ChoiceManager that it's too hard to tell what I changed.
Also, the splitting isn't actually "arbitrary": it's based on the splitting of choice adventures from the kolwiki's Choice Adventures by Number page.