*Excludes Observations that spanned multiple years
| Pre 1970 | 214 |
|---|---|
| 1970 | 28 |
| 1971 | 22 |
| 1972 | 15 |
| 1973 | 12 |
| 1974 | 19 |
| 1975 | 10 |
| 1976 | 12 |
| 1977 | 16 |
| 1978 | 10 |
| 1979 | 2 |
| 1980 | 6 |
| 1981 | 3 |
| 1982 | 5 |
| 1983 | 6 |
| 1984 | 4 |
| 1985 | 19 |
| 1986 | 18 |
| 1987 | 7 |
| 1988 | 111 |
| 1989 | 119 |
| 1990 | 87 |
| 1991 | 406 |
| 1992 | 253 |
| 1993 | 200 |
| 1994 | 562 |
| 1995 | 474 |
| 1996 | 293 |
| 1997 | 285 |
| 1998 | 355 |
| 1999 | 336 |
| 2000 | 707 |
| 2001 | 498 |
| 2002 | 602 |
| 2003 | 172 |
| 2004 | 101 |
| 2005 | 142 |
| 2006 | 260 |
| 2007 | 427 |
| 2008 | 828 |
| 2009 | 729 |
| 2010 | 380 |
| 2011 | 117 |
| 2012 | 150 |
| 2013 | 134 |
| 2014 | 93 |
| 2015 | 101 |
| 2016 | 79 |
| 2017 | 91 |
| 2018 | 66 |
| 2019 | 117 |
| 2020 | 77 |
| 2021 | 52 |
| 2022 | 87 |
| 2023 | 49 |
| 2024 | 96 |
| 2025 | 4 |
| Total | 10068 |