Generations of the Impala 
I have always thought of a generation of a car to mean specific body styles of a car. When a car's body style changes, it is a new generation (sorry if that sounds convulted, but ...).

Anyhow, the infoboxes stating the generations of the Impala may be wrong, and it may be worth checking out. For the record, here's how I understand the generations of the Impala: 1958 (first), 1959 (second), 1961 (third), 1965 (fourth), 1967 (fifth), 1969 (sixth), 1971 (seventh), 1977 (eighth), 1980 (ninth), 1994 (10th), 2000 (11th) and 2006 (12th).

Someone may want to look into this.