Earlier quoted context omitted.
Even assuming grandma is going to buy it herself, which probably isnt always practical, there's probably some people out there not thrilled about going to jail because grandma put pot in the console of the car or left it on the kitchen table and suddenly they have constructive possession without a card.
Right, but that's the thing: possession (even in the actual sense, let alone constructive possession) doesn't mean use. A card declaring (in effect) "I have been prescribed cannabis to use it as medicine" does mean use. If anything, Grandma being the card-carrying pot user and not you would likely be evidence in your favor - to be presented and argued by a competent defense attorney in court, of course, not by you to…
Was I an opiate user? If I just keep the script but never fill it am I more an opiate user than the guy on the street with a little baggy of white powder? People seek out and obtain scripts for stuff they never use, all the time.