Mike, I guess that is all correct from a particular modern point of view - I was merely distinguishing, simplistically, what the GWR differentiated, by virtue of its diagram types, between 'normal' passenger-carrying stock and stock designed to run with normal passenger stock but not designed to carry passengers (like Siphons). Horse boxes complicate the issue, because they were NPCCS but of course could carry human beings. TPOs are another interesting case, they carried humans but not passengers. A differentiation on the basis of gangway fitting is also somewhat fraught, because many full brakes (like a K22) were accessible to passengers passing through a train, whereas a gangwayed Siphon would be blocked to passengers as far as I know. The K diagrams were classed as 'Passenger Brake Vans'.
This is a interesting can of worms! (And possibly not for this thread.)