This rating was rather made for small extras(typically mini stories / short movies) that can be found on some DVDs.
e.g. http://www.imcdb.org/vehicle_5108-Dodge-Stealth-1991.html

Or some seen in the making-off and which have some interest to be listed.

The Limo example can be used for very special ones, e.g. http://www.imcdb.org/vehicle_230213-Renault-16-Stretched-Limousine.html
but indeed for common limos/motorhomes seen in extras it is not worth listing.