Qualifying scores for the National Exam vary from region to region because each region can only send the top X number of students from the Local Exam to take the National Exam. Consequently, there will be hypercompetitive regions such as California and New Jersey (in which you'll need to have a ridiculously high Local exam score to qualify) and fairly uncompetitive regions like Wyoming (I heard that one of the National Finalists a few years ago automatically qualified to take the National Exam no matter how he did on Locals because he and his friend were the only interested students in the region).