| Year | Count |
|---|---|
| 1964 | 5 |
| 1965 | 6 |
| 1966 | 8 |
| 1967 | 7 |
| 1969 | 9 |
| 1970 | 5 |
| 1971 | 6 |
| 1972 | 9 |
| 1973 | 7 |
| 1974 | 10 |
| 1975 | 5 |
| 1976 | 12 |
| 1977 | 32 |
| 1978 | 10 |
| 1979 | 26 |
| 1981 | 8 |
| 1982 | 11 |
| 1983 | 10 |
| 1984 | 11 |
| 1985 | 17 |
| 1986 | 13 |
| 1987 | 21 |
| 1988 | 24 |
| 1989 | 27 |
| 1990 | 28 |
| 1991 | 20 |
| 1992 | 22 |
| 1993 | 17 |
| 1994 | 16 |
| 1995 | 16 |
| 1996 | 11 |
| 1997 | 12 |
| 1998 | 11 |
| 1999 | 11 |
| 2000 | 12 |
| 2001 | 12 |
| 2002 | 11 |
| 2003 | 10 |
| 2004 | 5 |
| 2005 | 8 |
| 2006 | 9 |
| 2007 | 6 |
| 2008 | 13 |
| 2009 | 17 |
| 2010 | 6 |
| 2011 | 6 |