It was my understanding the Golden Anniversary Impala was a 1962 model commemorating the 50 years of Chevrolet not the 50 millionth Chevrolet made. Growing up as a kid, a friend of the family's ordered a 1962 Impala SS with a 409 and it was in 50th anniversary Gold. He always made a Big Deal about the "Special Color' because he owned a Body Shop and thought is was a unique car and color. I came across this in Hemmings:
https://www.hemmings.com/stories/art...evrolet-impala
I am by no means an expert, I'm just trying to learn here. Bill