Each state has different cutoffs, which can change from year to year. Basically, I think the goal is to take a proportional number of kids from each state, which means if you are from, say, NJ or California, you have much more competition than if you are from a lower-performing/less populous state. Kids who are outside the US, or who are boarding school students, are not included in specific states. The international students have to clear the highest state cutoff; I can’t remember the rule for boarding students, but I am pretty sure they are also held to a higher cutoff (but it might be regional, not sure).
There is a lot of informed discussion about NM on the Compass Prep blog by Art Sawyer; you can ask questions and he is very good about providing specifics when he can.
https://www.compassprep.com/national-merit-semifinalist-cutoffs/
