*Excludes Observations that spanned multiple years
| Pre 1970 | 6 |
|---|---|
| 1970 | 0 |
| 1971 | 5 |
| 1972 | 2 |
| 1973 | 0 |
| 1974 | 0 |
| 1975 | 0 |
| 1976 | 0 |
| 1977 | 1 |
| 1978 | 2 |
| 1979 | 3 |
| 1980 | 0 |
| 1981 | 0 |
| 1982 | 2 |
| 1983 | 1 |
| 1984 | 17 |
| 1985 | 138 |
| 1986 | 136 |
| 1987 | 275 |
| 1988 | 868 |
| 1989 | 69 |
| 1990 | 84 |
| 1991 | 350 |
| 1992 | 130 |
| 1993 | 539 |
| 1994 | 514 |
| 1995 | 195 |
| 1996 | 104 |
| 1997 | 71 |
| 1998 | 24 |
| 1999 | 147 |
| 2000 | 101 |
| 2001 | 48 |
| 2002 | 36 |
| 2003 | 110 |
| 2004 | 92 |
| 2005 | 106 |
| 2006 | 96 |
| 2007 | 93 |
| 2008 | 93 |
| 2009 | 101 |
| 2010 | 107 |
| 2011 | 102 |
| 2012 | 157 |
| 2013 | 124 |
| 2014 | 111 |
| 2015 | 98 |
| 2016 | 110 |
| 2017 | 96 |
| 2018 | 18 |
| 2019 | 49 |
| 2020 | 40 |
| 2021 | 50 |
| 2022 | 43 |
| 2023 | 60 |
| 2024 | 0 |
| Total | 5724 |