Invalidating an exam should let you scan it again, or add delete option.
Problem: We scanned a paper exam element marked as G instead of T, giving a failing grade. We fixed the G to a T and invalidated the exam. However, we could not scan it again since it was still seeing the prior exam. We had to grade the exam manually.
Solution: There should be an option to fully invalidate or delete an exam. I'm guessing the primary keys are the pin+test number. If so, another option would be to detect a change in the element and allow you to regrade it.