CooPay - I agree. It is phonetically derived from the original European term, "Coppe" (see below). The bastardized American term, "Coupe," gained widespread usage when the aforesaid thrusting executives took various linguistic liberties. Moreover, the error often is compounded -- for example, "Dian Coppe" becomes "Dinan Coupe" in non-Purist circles using the non-King's English. Fortunately, however, evidence still exists of proper usage, even in late-model applications - see immediately below, for example, for the proper, precise, and technically correct late-model application of the historically correct terminology, "Coppe" (pronounced CooPay).
Often, the sedan/coupe (coppe) distinction is easily ascertained. Typically for a "coupe" (coppe), you may expect to find a single pair of doors - "D's" for short - a lefty and a righty. For a sedan, however, it is more reasonable to expect twice that amount - Double D's - four in total (that's two lefty's and two righties). But it is not true in every case - and leave it to the Factory to confuse the Purists. Thereupon, sometimes we might find a single pair of D's, where double D's were expected -- and vice versa (see previous photo). Alas, "sedan" is probably correct in the following photo, since in all likelihood, there are more than two methods of entering this particular model.
Good luck in your search, for a Sedan or a Coppe. A word of caution - on older S models, sometimes the double D's tend to sag. Nothing that can't be fixed, of course.