1975–80
(seasons 1, 2, 3, 4, 5)
1980–85
(seasons 6, 7, 8, 9, 10)
1985–90
(seasons 11, 12, 13, 14, 15)
1990–95
(seasons 16, 17, 18, 19, 20)
1995–2000
(seasons 21, 22, 23, 24, 25)
2000–05
(seasons 26, 27, 28, 29, 30)
2005–10
(seasons 31, 32, 33, 34, 35)
2010–15
(seasons 36, 37, 38, 39, 40)
2015–present
(seasons 41, 42)