You know what he's right (via Wikipedia and drumroll...HPS lol). . .I'm going to push the change to be (depending on number of cars) to the classes of...combining 74-93.

First Generation - 1964 1/2 to 1973

Second/Third Generation - 1974 to 1993

Fourth Generation - 1994 to 2004

Fifth Generation - 2005 to 2008