In the strictest reading, the luminaire is *not* part of the building finish, otherwise you could not have an old work can.
When you take that old work can logic to it's logical conclusion you could have to remove any part of a luminaire or other equipment to get to the box behind it.
If some crafty carpenter came along behind you and put a little piece of trim around that light that kept you from removing it, you are not accessible anymore.
