MAA的官方说法是all scorers, cut off 是由所有考生成绩定的，并只不限于美国考生

https://www.maa.org/math-competitions/invitational-competitions

1. Q. How do I qualify for the AIME?

   A. Qualification parameters for AIME vary with the results of the AMC 10/12 competitions. For AMC 10, invitations are issued to at least the top 2.5% of all scorers. For AMC 12, invitations are issued to at least the top 5% of all scorers. The exact cutoffs will depend on the difficulty of each competition.