To identify parking spaces designed specifically for disabled people (where only disabled people are allowed to park), I’ve used amenity=parking_space + dissabled=designated. It is simple and (to me) clear.
Yes, but this is about the whole parking area, not the specific single parking spaces.
This seems to me not addressing the fact that the parking space allows access only to disabled persons (where instead disabled=designated is for that).
Ale
In general I map each disabled parking space individually using amenity=parking_space, as I don’t thing amenity=parking works very well on its own. In Spain they are painted blue and scattered throughout most towns.