*Excludes Observations that spanned multiple years
| Pre 1970 | 214 |
|---|---|
| 1970 | 46 |
| 1971 | 44 |
| 1972 | 24 |
| 1973 | 22 |
| 1974 | 49 |
| 1975 | 18 |
| 1976 | 7 |
| 1977 | 14 |
| 1978 | 40 |
| 1979 | 83 |
| 1980 | 5 |
| 1981 | 70 |
| 1982 | 12 |
| 1983 | 14 |
| 1984 | 36 |
| 1985 | 20 |
| 1986 | 20 |
| 1987 | 10 |
| 1988 | 33 |
| 1989 | 72 |
| 1990 | 59 |
| 1991 | 52 |
| 1992 | 37 |
| 1993 | 66 |
| 1994 | 80 |
| 1995 | 95 |
| 1996 | 81 |
| 1997 | 76 |
| 1998 | 97 |
| 1999 | 172 |
| 2000 | 291 |
| 2001 | 354 |
| 2002 | 240 |
| 2003 | 186 |
| 2004 | 134 |
| 2005 | 125 |
| 2006 | 188 |
| 2007 | 168 |
| 2008 | 162 |
| 2009 | 179 |
| 2010 | 121 |
| 2011 | 123 |
| 2012 | 131 |
| 2013 | 130 |
| 2014 | 180 |
| 2015 | 151 |
| 2016 | 115 |
| 2017 | 99 |
| 2018 | 114 |
| 2019 | 118 |
| 2020 | 103 |
| 2021 | 98 |
| 2022 | 130 |
| 2023 | 68 |
| 2024 | 43 |
| Total | 5419 |