You could argue that the first few sittings are experimental as they figure our appropriate exsm length/format. Lets say this sitting exams are judged too long. They lower pass mark and more candidates pass because there is no way to distinguish those who could not finish from those who didn’t know how to do it. This could show a higher pass ratio (wishful thinking 😉 ). Next sitting pass ratio could be drastically different and could lead to questions.