Shared driveways are documented in the wiki as pipestems and have three competing tagging schemes, all more descriptive than driveway2.
What you are attempting to do here is override the generally understood meaning of driveway with one from a niche legal (re)definition in one corner of the United States. How the Californian legislature twists the meaning of a word is not generally useful to a global project and is doubly useless to a project that prefers British English anyway. You have been told this before and a repeated refusal to respect OSM’s longest standing tagging principles comes across as bad faith. Yes, you may say it’s an alternate definition, but in that case we may as well call it service=motorway under a new definition of motorway as “anything a motorised vehicle can fit down”.
From Cambridge online:
driveway
noun[C]
a private area in front of a house or other building onto which you can drive and park your car
…
driveway | American Dictionary
noun [ C ]
a short private road that leads from a street to a person’s house or garage (= building where a car is kept)
Merriam Webster gives:
driveway
noun
: a private road giving access from a public way to a building on abutting grounds
… First Known Use 1845, in the meaning defined above
Which is a slightly broader definition, but doesn’t really cover service roads whose purpose is to lead to other surface roads.
If we need a point of distinction I’d probably say that per the Cambridge definitions parking on driveways is usually expected, but the service ways to these larger facilities do not (usually) permit parking on them, they lead to parking or other service ways types.
IMO the argument for driveway2 is like passionately arguing that something should be tagged as a duck because of the feathers, webbed feat and general beak shape, while completely ignoring the fact that the animal in question is actually a goose. Arguing about mandatory and optional clauses in a project that doesn’t document things that way is somewhat missing the point.