Year	Number
1970	40
1971	36
1972	33
1973	31
1974	29
1975	27
1976	25
1977	24
1978	23
1979	22
1980	21
1981	21
1982	21
1983	22
1984	20
1985	20
1986	20
1987	18
1988	19
1989	19
1990	18
1991	18
1992	19
1993	19
1994	18
1995	17
1996	16
1997	16
1998	16
1999	18
2000	17
2001	19
2002	18
2003	17
2004	18
2005	18
2006	19
2007	19
2008	20
2009	19
2010	20
2011	20
2012	20
2013	20
2014	20
2015	22
2016	21
2017	22
2018	22
2019	23
2020	24
2021	24
2022	25