The fourth-generation Cadillac Series 62 arrived for 1954 with wraparound glass, reverse gull-wing bumpers and a dual exhaust routed straight through the rear bumper, then spent three years breaking its own sales records. Along the way it went from a 17.3-second run to 60 mph to a flat 12 seconds. Here is how to tell a 1954 from a 1955 from a 1956, and what the differences actually mean.