It's not a rigid stance. When you look directly at the percentile chart, it literally shows there is a tiny difference at the highest ranges. For example, 519-528 differ by two percentiles. Take that difference of 9 points at the midrange and you get a range from 34th to 68th percentiles. An extreme example is will adcoms ever say anything like "This guy got a 519, but this other guy got a 525 so he's probably better". Probably not. It will be a few years before they can even use the new MCAT to its fullest potential so right now, it's more of a "this guy is ______ above the mean score of 500".
The "proof" of a minimum MCAT has always existed. Nearly every medical school says what they screen out and they list their matriculate data. There have been standards for the longest time. Of course schools accept students below these standards, but it is rare and these students are usually URM, business owners, dragon slayers, etc. If you want to use the old standard of 30 is the "good" score, that means 509 (80th percentile). Human tendencies in being slightly OCD means 510. 500 and above is acceptable right now but it definitely will not be next cycle. This doesn't take data to figure out. It's common sense.
https://aamc-orange.global.ssl.fast...-4aa0-90cb-70184be8c8b8/percentilenewmcat.pdf