I was quoting a post that mentioned 99.999th percentile. Nobody lists that level of precision in SAT/ACT/… because the tests don’t distinguish that level of precision. If you had some way of distinguishing the best per 100,000 students, such as USAMO, then I’d expect you’d find few of this group at Mudd because they are so rare. The point was talking about the difference between 90th and 99.999th percentile is irrelevant since hardly any of either group are at Mudd.