Self-studying can lead to not being able to find a seat for the exam. For example, our dd is taking Purdue’s CS 180 HS class which prepares students for the AP CS A exam. Finding a local school offering the exam that will allow her a seat is another issue. Some schools refuse to let you sit in on the exam. There is only 1 school anywhere in our area offering it. If they won’t let her take it with their students, she won’t be able to take it. (I’m waiting until after the PSAT to call bc I figure that is their primary focus right now.) Even finding a local school offering some APs like AP Latin or both physics C exams can difficult. So it can be a case that the student completed the equivalent coursework but can’t take the test. (I realize our scenario is atypical, but amg homeschoolers, the issues exist. No simple generalities.)