Actually, the 25%-ile in the current MSAR is 519, and that means 519 and below, not just below 519, or 518. 10%-ile is 517. Nationally, that is 94%-ile, but it is 10%-ile at NYU. Of course, there are always outliers with spectacular X-factors (a whopping 13 or so who have MCATs at or below 517), but I respectfully stand by what I said.
By the way, I doubt there are people at NYU with 525+ and nothing else. A full half the class is above 522, and I'm pretty sure all of them have X-factors as well. To me, it really does look like you either have the numbers or you don't, given how high all of their numbers are, even the 10%-ile. The vast majority of the people with the numbers also don't really have a prayer, given how many people have the numbers (probably around 2,500 at 520 or above) and how small the class is.
Congratulations on receiving the II. You are definitely an outlier, just based on the reported numbers. I wish you all the luck in the world, but, until you receive an A, you are not part of that 10%, regardless of how spectacular your X-factor is. Around 1,000 people receive IIs, but only around 135 or so receive As. If you do receive an A with a 516, you will be part of a very special group (around 13 out of 10,000+ applicants), and 516 is a pretty damn high 92%ile in its own right.