Requiring exam bodies and universities to return all marked-up exam papers would reduce the risk of mistakes or oversights. If there has been a mistake, students should notice immediately. Some institutions return marked-up exams on request, for a fee. They should be returned unconditionally.
If a face-to-face exam is recorded, a copy of the recording should be given to the student. There are additional benefits. It should also provide feedback on performance, and gives the examining body great protection against allegations of bias or prejudice. If you have failed it’s easier to accept. It should simplify any appeals process. It should protect students from any intentional or unintentional bias.