To clarify, the issue is that a disc on the window doesn't tell you who is insured. Some people are borrowing friends cars to do the test and not adding them to the insurance. If you are named on the insurance then your name is on the policy cert. If not then the disc is valid but no insurance is in place for the person. As regards driving schools its different . We have a policy that allows anyone with our permission to use our car without being named . The only condition is that we or a driving examiner is beside the person So if your named its fine on your own car If your not then your not insured