Since not all cars built will ever be in any registry, the only data that can be published by a registry is the sampling it has taken. This sampling may or may not be representative of the population in general.
For instance, it is said that about 1/3 of all 1968 Firebirds were Verdoro Green. Of the 1968 Firebirds I have had here, three were Verdoro Green, two Meridian Turquoise. Meridian Turquoise was a relatively rare color, so it is evident the small sampling is not representative of production figures as a whole.
My '67 was Coronado Gold, a rare spring color, and my '69 is Goldenrod Yellow, a special order uncommon color.
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching