7. Unless used on a public highway, a road vehicle stocked by the manufacturer or delivered by him to a dealer, as well as a road vehicle entrusted to the management of the public curator, or in the possession of a dealer holding it in stock for sale, is exempt from registration. The same rule applies to a road vehicle impounded, confiscated or seized by a peace officer as well as to a discarded road vehicle the registration certificate and identification number of which have been remitted to the Régie.