Have you tried ichang papeda seedlings? I wonder whether or not the same situation would occur to ichang papeda when it was young.
I have an update and can answer that question now.
I grew a seed from an Ichang papeda fruit. (This is the tree in Portland that I have previously described in other posts, not surrounded by any other citrus trees)
This is my first time actually growing Ichang papeda from seed.
I have just checked on it right now, and the a little seedling has sprouted up with four little leaves.
But here is the interesting thing: all of those little leaves have absolutely no trace of winged petioles! They are completely single leaves.
This seems very bizarre to me. I've grown numerous different Ichang papeda hybrids from seed before (well, nearly all of them I think, Yuzu, N1tri, numerous Ichangquat seedlings). They all had at least some winged petiole on the leaves when the seedling first sprouted.
All of my very small Ichang papeda cuttings that I grew also sprouted leaves with fairly big sized winged petioles, even though the cutting may have been very small (like 3 inches).
So it appears you might be right. This is very strange.
This is only one seedling, so I can't say for sure whether this would be a pattern.
And I am absolutely sure this seed came from an Ichang papeda fruit. I have not very recently grown anything else from seed, so there is no possibility there could have been an accidental mix-up.