I had this doubt too; actually the history of mk IV name's birth is not so detailed and easy to obtain, but this Van den Plas DHC, that some years ago has been restored and painted in silver and metallic blue, seems to be called mk IV everywhere. Doubts I was talking about concern the fact that this name, universally used, is correct or not; the advertise leaf I posted doesn't use neither mk IV nor mk V denomination,and I think this depend on the fact that mk IV denomination was not an official one, but it began to be used to identify 1,5-2,5-3,5 litre (ex SS) after mk V appeared. So, why don't call this car "Jaguar 3.5 litre DHC Van den Plas, 1947"?