You're right. He moved on after the 64/65 season. He began with the very first regular show I believe, in 1960. Won 5 Emmies in a row, too. Always gave credit to "the big guy" (Andy) for his success. As I recall, at one Emmey award he said, "Well, if it wasn't for the Big Guy, I would be parking cars out here tonight".
One of the few shows I'll take the time to watch on television. And I'm 22! ha!
God bless you, Don Knotts. You've made a lot of people smile through the years.