*Excludes Observations that spanned multiple years
| Pre 1970 | 52 |
|---|---|
| 1970 | 7 |
| 1971 | 3 |
| 1972 | 4 |
| 1973 | 5 |
| 1974 | 5 |
| 1975 | 3 |
| 1976 | 2 |
| 1977 | 5 |
| 1978 | 8 |
| 1979 | 12 |
| 1980 | 13 |
| 1981 | 9 |
| 1982 | 12 |
| 1983 | 22 |
| 1984 | 39 |
| 1985 | 31 |
| 1986 | 44 |
| 1987 | 56 |
| 1988 | 72 |
| 1989 | 60 |
| 1990 | 60 |
| 1991 | 62 |
| 1992 | 76 |
| 1993 | 67 |
| 1994 | 65 |
| 1995 | 118 |
| 1996 | 114 |
| 1997 | 119 |
| 1998 | 102 |
| 1999 | 98 |
| 2000 | 100 |
| 2001 | 113 |
| 2002 | 103 |
| 2003 | 114 |
| 2004 | 114 |
| 2005 | 133 |
| 2006 | 129 |
| 2007 | 126 |
| 2008 | 106 |
| 2009 | 110 |
| 2010 | 142 |
| 2011 | 156 |
| 2012 | 175 |
| 2013 | 173 |
| 2014 | 195 |
| 2015 | 184 |
| 2016 | 185 |
| 2017 | 165 |
| 2018 | 156 |
| 2019 | 139 |
| 2020 | 140 |
| 2021 | 136 |
| 2022 | 110 |
| 2023 | 8 |
| 2024 | 3 |
| Total | 4560 |