It all boils down to whether you want to take on the government in court. You might be a little safer with an up to date authorization but not really by much. If the thugs come knocking on your door it won't really matter what you have in the way of documentation, they'll just drag your ass into court.
All you have to prove in court is whether you have a valid qualifying condition, the authorization won't mean much if your doctor didn't adequately put the qualifying condition in his chart notes. In this day and age both you and your doctor have to be attorneys to protect yourself from oppression.