Yes you can yes you can fill improvement of a 12 subjects as you want you can fill the improvement of one subject two subject 3 subject and all the subject you want it is information that you will never get from any other sources such as a if you call to the Mohali PSEB main Centre you can never get this information you will never get information from internet but I know this information because I had filled by improvement exam in 2023 ok there are two chance in which it is held first candidate improvement exam