Enrolment

I'm somewhat at a loss as to where to post this question, or even how to search to see if someone else had a similar problem. Here's the situation:

I have a series of Benchmark exams that we have our students take before being accepted into the program. Set up as a quiz within a course set up exclusively just for these Benchmarks. So - the course only contains 6 quizzes and nothing else.

The student self-enrols into the Benchmark course, is given a password for the Benchmark quiz they're supposed to take, and then - that's it. From the results we determine future steps.

But that "course" never actually ends. New students enrol in it, old ones expire and drop out.

My question is... those students who expire and become unenrolled - I lose their grade for that benchmark quiz. Is there any way to recover the score? I've tried moving the student back into the course - but the scores aren't recovered.