*Excludes Observations that spanned multiple years
| Pre 1970 | 72 |
|---|---|
| 1970 | 181 |
| 1971 | 163 |
| 1972 | 195 |
| 1973 | 52 |
| 1974 | 93 |
| 1975 | 105 |
| 1976 | 53 |
| 1977 | 74 |
| 1978 | 93 |
| 1979 | 24 |
| 1980 | 35 |
| 1981 | 124 |
| 1982 | 42 |
| 1983 | 29 |
| 1984 | 71 |
| 1985 | 40 |
| 1986 | 17 |
| 1987 | 5 |
| 1988 | 152 |
| 1989 | 168 |
| 1990 | 157 |
| 1991 | 161 |
| 1992 | 133 |
| 1993 | 639 |
| 1994 | 355 |
| 1995 | 306 |
| 1996 | 183 |
| 1997 | 145 |
| 1998 | 115 |
| 1999 | 203 |
| 2000 | 330 |
| 2001 | 225 |
| 2002 | 222 |
| 2003 | 105 |
| 2004 | 32 |
| 2005 | 100 |
| 2006 | 179 |
| 2007 | 267 |
| 2008 | 158 |
| 2009 | 108 |
| 2010 | 119 |
| 2011 | 117 |
| 2012 | 106 |
| 2013 | 149 |
| 2014 | 79 |
| 2015 | 35 |
| 2016 | 44 |
| 2017 | 38 |
| 2018 | 49 |
| 2019 | 73 |
| 2020 | 46 |
| 2021 | 37 |
| 2022 | 62 |
| 2023 | 30 |
| 2024 | 1 |
| Total | 6896 |