FWIW from what I saw as an earlier X who went back to school again and then grad school after as well. It seemed to me like the real shift out of Xennial didn't fully happen until those born maybe kinda around 1986ish started arriving on campus. Suddenly tight jeans, bright colors, preppy (as well as some participation trophy type attitudes) and more acceptance of pop music for guys and less angst and stuff showed up (this stuff, aside from the participation trophy stuff and the getting even yet more uptight about various things, which were much less OG X like, was actually trending a bit back more early X like where fashion was colorful, tight, wild, flashy and music not hard alt/rock/grungy and more pop dominated and to when there had been less difference between what girls vs guys listened to than seemed to be the case for Xennials, not all the way back by any means but a bit back).

Now there was a slow shift towards more pop and less angst going from around 1982-1985 born but the full on style changes and fully new attitudes and stuff didn't seem to really hit college campus until around 2005ish.

While 1984 were a bit shifting more Millennial to me overall they still seemed a lot closer overall tied to Xennials than to core, much less, late Millennials. Style still seemed 100% Xennial. Zero participation trophy type attitude in evidence yet.

I'll also say that Xennials had definitely shifted way away from earlier X though. Man oh man did style and some attitudes change from late 80s/earliest 90s college times. Style was almost 100% opposite and music tastes for guys were almost 100% opposite too (at least in public, some did have secret playlists that trended a little bit more back X like, but Xennial era seemed to have a lot of rules that made people afraid of losing either "street cred" or "alt/indie cred" which was a touch ironic in the suppose era of freedom/individuality/authenticity/etc. in many ways 80s mainstream actually felt a lot more diverse, varied and free in some ways, but it's complex). And you could really notice how Xennials got changed by having been first generation to have been raised on non-stop scare media and the first initial rise of school shootings too. and it seemed quite noticeable that it was a generation raised around grunge and gangster rap from a young age vs. one that had zilch of that influence at all.

Xennials all seemed closer to each other than either earlier X or core/later Millennials. Maybe roughly '77-'85 as a group. Although shifting some along the way in various ways. And the X side a little distinct from the Millennial side. But overall still all closer to each other than to their own respective generations. The Xennial style was certainly utterly almost beyond 100% opposite of Gen X but also considerably different, if to a somewhat lesser degree, than a good chunk of core/later Millennial style. Some attitudes and vibes were closer to X and others closer to Millennials and sometimes not really quite like either. In general there were some ways Xennials were closer to X than Millennials were for sure, but interestingly also some ways Millennials were actually closer to X than Xennials were. Xennials seemed to have a really deep knowledge of the movies and TV from right before their time, tons of knowledge of 80s tv/movies and many even still listed 80s teen movies like Ferris Bueller as their favorite over ones from say the late 90s and more their time. Millennials were probably good about knowing prior stuff too but probably a bit shy of the degree that Xennials did who maybe knew the most of the just prior gens teen films and general movies and all than any micro-gen in recent times has. That said all this generational stuff is always very vague and fuzzy and all a bit iffy stuff and so complex it would take dozens more paragraphs to begin to work out more fully and anyway whatever you do named generations never really entirely work out or quite make sense.

Gen Y used to be along the lines of 1975-1985ish. But it kind of varied all over starting as early as 1973 and as late as 1979 and sometimes a vague unspecified ending.