The skinny on Perfect is this:
It is bundled down onto permanent ACR after hitting the 3 years since release mark. The only reason that didn't happen back in March was because it received a manual reset in September 2017 when it was formally promoted as a single. This had the effect of resetting the timer, so its "official" release date was mid-September that year. Meaning we have just hit the third anniversary of that moment.
This isn't an arbitrary or spontaneous application of the rules, it happens automatically to every single track in the database the moment they reach the three year mark, it is just that Perfect has uniquely and extraordinarily been in a position to be charting when that happened so we all got to witness it.