*Excludes Observations that spanned multiple years
| Pre 1970 | 174 |
|---|---|
| 1970 | 5 |
| 1971 | 8 |
| 1972 | 8 |
| 1973 | 2 |
| 1974 | 2 |
| 1975 | 4 |
| 1976 | 1 |
| 1977 | 3 |
| 1978 | 10 |
| 1979 | 12 |
| 1980 | 7 |
| 1981 | 2 |
| 1982 | 5 |
| 1983 | 1 |
| 1984 | 8 |
| 1985 | 61 |
| 1986 | 13 |
| 1987 | 157 |
| 1988 | 322 |
| 1989 | 79 |
| 1990 | 42 |
| 1991 | 201 |
| 1992 | 129 |
| 1993 | 198 |
| 1994 | 147 |
| 1995 | 334 |
| 1996 | 256 |
| 1997 | 103 |
| 1998 | 19 |
| 1999 | 69 |
| 2000 | 97 |
| 2001 | 97 |
| 2002 | 54 |
| 2003 | 88 |
| 2004 | 135 |
| 2005 | 108 |
| 2006 | 93 |
| 2007 | 131 |
| 2008 | 165 |
| 2009 | 152 |
| 2010 | 107 |
| 2011 | 117 |
| 2012 | 138 |
| 2013 | 161 |
| 2014 | 138 |
| 2015 | 127 |
| 2016 | 87 |
| 2017 | 115 |
| 2018 | 94 |
| 2019 | 57 |
| 2020 | 51 |
| 2021 | 67 |
| 2022 | 99 |
| 2023 | 93 |
| 2024 | 91 |
| 2025 | 128 |
| 2026 | 3 |
| Total | 5175 |