Unless you have a build sheet saying 9676 or the car can be certified as an undisturbed original paint car, the high spoiler could have been added at any time over the car's life. The spoiler existed because of the car below - it had to be homologated for the 1970 Chaparrel Z28 Trans-Am cars, which meant offering it as a factory-installed option.
The high spoiler carried on as an option in 1971 and 1972, you had to order it as D80. Further, in 1972 if you didn't specifically order your Z with D80 you got no spoilers at all. Ever see a bare-back '72 Z28? It's weird. Looks like a shaved cat. They used one in the ad below...
