*Excludes Observations that spanned multiple years
| Pre 1970 | 145 |
|---|---|
| 1970 | 4 |
| 1971 | 2 |
| 1972 | 1 |
| 1973 | 1 |
| 1974 | 2 |
| 1975 | 4 |
| 1976 | 2 |
| 1977 | 3 |
| 1978 | 1 |
| 1979 | 6 |
| 1980 | 2 |
| 1981 | 2 |
| 1982 | 1 |
| 1983 | 2 |
| 1984 | 5 |
| 1985 | 53 |
| 1986 | 72 |
| 1987 | 146 |
| 1988 | 298 |
| 1989 | 45 |
| 1990 | 19 |
| 1991 | 194 |
| 1992 | 63 |
| 1993 | 390 |
| 1994 | 255 |
| 1995 | 269 |
| 1996 | 152 |
| 1997 | 95 |
| 1998 | 15 |
| 1999 | 91 |
| 2000 | 88 |
| 2001 | 66 |
| 2002 | 49 |
| 2003 | 80 |
| 2004 | 87 |
| 2005 | 95 |
| 2006 | 69 |
| 2007 | 84 |
| 2008 | 97 |
| 2009 | 83 |
| 2010 | 108 |
| 2011 | 86 |
| 2012 | 111 |
| 2013 | 96 |
| 2014 | 101 |
| 2015 | 109 |
| 2016 | 105 |
| 2017 | 96 |
| 2018 | 59 |
| 2019 | 45 |
| 2020 | 38 |
| 2021 | 118 |
| 2022 | 79 |
| 2023 | 56 |
| 2024 | 12 |
| Total | 4357 |