| Year | Count |
|---|---|
| 1971 | 7 |
| 1973 | 5 |
| 1974 | 6 |
| 1975 | 9 |
| 1976 | 10 |
| 1977 | 9 |
| 1978 | 16 |
| 1979 | 18 |
| 1980 | 18 |
| 1981 | 20 |
| 1982 | 13 |
| 1983 | 21 |
| 1984 | 12 |
| 1985 | 27 |
| 1986 | 13 |
| 1987 | 22 |
| 1988 | 17 |
| 1989 | 14 |
| 1990 | 14 |
| 1991 | 15 |
| 1992 | 15 |
| 1993 | 16 |
| 1994 | 18 |
| 1995 | 10 |
| 1996 | 16 |
| 1997 | 13 |
| 1998 | 18 |
| 1999 | 11 |
| 2000 | 10 |
| 2001 | 14 |
| 2002 | 7 |
| 2003 | 9 |
| 2004 | 12 |
| 2005 | 11 |
| 2006 | 9 |
| 2007 | 13 |
| 2009 | 10 |
| 2010 | 7 |
| 2011 | 9 |
| 2012 | 9 |
| 2013 | 9 |
| 2014 | 5 |