*Excludes Observations that spanned multiple years
| Pre 1970 | 4 |
|---|---|
| 1970 | 0 |
| 1971 | 5 |
| 1972 | 0 |
| 1973 | 0 |
| 1974 | 2 |
| 1975 | 0 |
| 1976 | 0 |
| 1977 | 5 |
| 1978 | 3 |
| 1979 | 3 |
| 1980 | 2 |
| 1981 | 0 |
| 1982 | 0 |
| 1983 | 1 |
| 1984 | 1 |
| 1985 | 91 |
| 1986 | 76 |
| 1987 | 134 |
| 1988 | 275 |
| 1989 | 102 |
| 1990 | 43 |
| 1991 | 210 |
| 1992 | 262 |
| 1993 | 476 |
| 1994 | 470 |
| 1995 | 486 |
| 1996 | 289 |
| 1997 | 219 |
| 1998 | 73 |
| 1999 | 190 |
| 2000 | 116 |
| 2001 | 200 |
| 2002 | 95 |
| 2003 | 142 |
| 2004 | 161 |
| 2005 | 209 |
| 2006 | 150 |
| 2007 | 187 |
| 2008 | 168 |
| 2009 | 145 |
| 2010 | 167 |
| 2011 | 153 |
| 2012 | 189 |
| 2013 | 167 |
| 2014 | 174 |
| 2015 | 184 |
| 2016 | 202 |
| 2017 | 183 |
| 2018 | 124 |
| 2019 | 157 |
| 2020 | 71 |
| 2021 | 102 |
| 2022 | 219 |
| 2023 | 11 |
| 2024 | 0 |
| Total | 7098 |