Whatever that number is, I suppose it's up to the medical profession to establish whether it's a critical illness or a terminal illness and report that to the courts. Then it's for the judge to decide if there are one, two, or thirty-some, as you indicate. I think that would have to be taken into consideration.
I'm trying to get my head around your suggestion that there may be too many definitions of critically ill to allow this to work. I don't think that would matter. If the doctor has indicated this is the case, that's the way it would be, regardless of what the illness was.