The magazines have made a lot of hay with the whole 1 of X deal. Unlike the other 2 major manufacturers of the era, Mopar was so kind as to allow anyone to buy anything in any configuration (almost) which has resulted in virtually no 2 cars identical in every aspect. That said, the investor types (and the decoder types) have turned this issue into cash by offering scarcity as a price driver. It works good on a non Mopar person; "my 73 slant six dart is only 1 of 2 known to exist with an am radio and bucket seats with the radiator sticker on the left side".... (no I don't have a 73 Dart). Once you get away from the major items such as engine, trans, rear axle, color and perhaps seats it becomes a bit silly. Its the pyramid effect; the more items considered the rarer a car becomes; unfortunately there is no way to verify any aspect of it other than the "authenticator" type people who have made a career of telling people how rare their car is which brings illusions of Barrett Jackson gold.
sorry for the rant; its a bit of a sore spot with me