This car has a personal license plate, CSG1, which is for the Commonwealth Secretary General. The car has the rubber block bumpers, so it dates from after November 1976. Several DS420 limos have carried that license number in time sequence; the last one in the factory notes is from November 1982. A comment on the Flickr photo site states that the number is still in use, and shows a recent photo with a high end BMW carrying it.

Contributed from the Flickr photo hosting account of Trigger's Retro Road Tests. Used with permission.