The first special, Julie and Carol at Carnegie Hall, was aired in 1962.
[1] The inclusion of Ball was partly because CBS insisted on Burnett having an established co-star for the special, and also because Ball already had a contract with CBS for up to three specials (in addition to her regular sitcom The Lucy Show) for the 1966–67 season, of which she would only produce one (Lucy in London).
The variety / sketch comedy was such a critical and ratings success that CBS rebroadcast it on January 15, 1967.
[3] In April 2016, MeTV broadcast the special for the first time in 50 years.
Data is from Carol Burnett: The Special Years (CBS, 1994).