In undergraduate colleges and universities, graduates are usually required to take CET-4 (certificate issued by the Ministry of Education), and CET-6 is the highest level for non-English majors.
College English majors usually require graduates to take CET-4, and the highest level of English majors is TEM-8.
The professional level 4 is equivalent to the non-professional level 5.5, and there is no level 5 in the exam, which is just a measure.
I believe you will be satisfied with this answer. In short, 356 refers to a section. There is no need to set up exams at different levels, otherwise it will be too rigid, don't you think?
I hope I can solve your problem.