Okay, that makes sense. "Retcon" just doesn't seem like the right term for it.
Anyway, YX's lack of pointed ears supports my idea that some change occurred in his heart to cause him to name himself "Xehanort" and become the scheming old man he is now. Considering how MX filled every seat with a completely different version of himself, except, seemingly for YX. That suggests to me that you can't bring several of the exact same person through time together, so I think YX is a different form of Xehanort altogether.
Retcon is in general a term that, while in essence neutral, has got at least in western media a very negative vibe because of too radical nostalgia junkies bitching about every little change (it's not only in KH) when it is actually pretty obvious that a story that is still in development and not finished evolves and changes over time, which can
also involve changes to already established material.
Some issues may have been foreshadowed subtly or were simply vague enough to allow different interpretations and explanations, and then any change made to it actually flows into the overall narrative pretty seamless.
It actually also allows to experience the older entries with a completely new outlook and look for other tiny things that may offer different explanations which may or may not addressed in the future.
Ansem SoD's
skin color is however really such a minuscule detail that really doesn't need to be made much fuss about.
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Anyways, back to topic on "Xehanort's ears", it's a funny little tidbit that they either apparently deliberately seem to want to throw us off with the ears or we fans are just overanalyzing things since Nomura himself only ever placed much emphasis on the
golden eyes and whenever they want to hammer in some exposure of "there is Xehanort influence in there" they zoom in on the golden eyes, like with Vanitas in BBS and Braig/Xigbar in both BBS and DDD.
The ears are almost totally ignored and yet there is that discrepancy with Young Xehanort (compared to the rest of the "true" Xehanort's, not possessed vessels) and Xaldin/Dilan, who has the pointed ears but
not the golden Xehanort eyes that seem to be a main indicator of heavy Xehanort influence.
So Xaldin maybe had less Xehanort-influence than Xigbar and Saix, but more than i.e. Zexion, Lexaeus or Marluxia? I remember when possessed by Ansem and while being the most susceptible to Darkness Riku never showed any signs of golden eyes or pointed ears (or rather, you could never see the upper parts of Riku's ears because they were always hidden beneath some hair).
Vanitas is also a curious case since he definitely does have the golden eyes but we cannot check his ears because they're hidden by that metal jaw-thingy from his helmet.
The theory that Young MX might have been at least a little more down to earth and not the sociopath incapable of empathy we see in old MX (and largely in Xemnas and Ansem SoD as well) is in so far plausible as that at least in the beginning when training together (before they were both named Masters and Xehanort was consumed in his thirst for knowledge and abandoned his armor) Young Xehanort and Eraqus must have had some sort of bond because otherwise they wouldn't have called each other "brother" and if Xehanort was already the cold-hearted manipulative bastard he's now he would probably not have been made Master in the first place.
That each Xehanort, even of the "true" Xehanorts, is somehow different gets also somewhat emphasized with the whole quartet of MX, YX, Ansem and Xemnas, as despite all their similarities they have some notable differences, Young Xehanort even more than the other three.
Nomura surely is milking the "Another" anagram of Xehanort's name for all that's worth, probably even more than all the other anagrams you can form from his name, even outlasting "no heart" which arguably describes older Xehanort's entire being since he treats hearts "like bottles on a shelf" and not as the proofs of life and manifestations of a persons spirit that they really are.