• 1950 to 1954 2
• 1955 to 1959 3
• 1960 to 1964 4
• 1965 to 1969 5
• 1970 to 1974 4
• 1975 to 1979 4
• 1980 to 1984 4
• 1985 to 1989 4
• 1990 to 1992 1