I've known people who have gone to court with old authorizations and the judge said he wanted more recent records. I agree that the language of the law doesn't specify one should need to renew every year explicitly. In fact the language just uses passed tense, "has been diagnosed"..."has been advised"....but even still I would keep current records, and if not receive a new recommendation every year, just ensure you are getting check ups with that doctor every now and then. If you don't you may end up having to go back and get them to resign off on your condition, to satisfy a judge. You need to look at it from the position of the state, and they are going to see marijuana use as more egregious than schedule 2 drugs (like morphine ROFL). That's going to be their perspective.

But when it comes to doctors that explicitly state an expiration date, I don't see any wiggle room. A doctor can withdraw their medical opinion, and you'd be up shit's creek in front of a prosecutor if your doctor wouldn't get your back in court. In fact if he testified that he felt you no qualified I think you'd be done in front of a judge or jury. Unless you had another doctor to back you up.