*Excludes Observations that spanned multiple years
| Pre 1970 | 118 |
|---|---|
| 1970 | 23 |
| 1971 | 17 |
| 1972 | 17 |
| 1973 | 19 |
| 1974 | 12 |
| 1975 | 13 |
| 1976 | 6 |
| 1977 | 9 |
| 1978 | 7 |
| 1979 | 7 |
| 1980 | 17 |
| 1981 | 28 |
| 1982 | 8 |
| 1983 | 26 |
| 1984 | 25 |
| 1985 | 32 |
| 1986 | 9 |
| 1987 | 25 |
| 1988 | 168 |
| 1989 | 136 |
| 1990 | 36 |
| 1991 | 81 |
| 1992 | 65 |
| 1993 | 108 |
| 1994 | 164 |
| 1995 | 154 |
| 1996 | 120 |
| 1997 | 157 |
| 1998 | 110 |
| 1999 | 411 |
| 2000 | 111 |
| 2001 | 156 |
| 2002 | 517 |
| 2003 | 268 |
| 2004 | 157 |
| 2005 | 61 |
| 2006 | 150 |
| 2007 | 329 |
| 2008 | 354 |
| 2009 | 292 |
| 2010 | 206 |
| 2011 | 61 |
| 2012 | 106 |
| 2013 | 79 |
| 2014 | 84 |
| 2015 | 78 |
| 2016 | 141 |
| 2017 | 79 |
| 2018 | 79 |
| 2019 | 113 |
| 2020 | 29 |
| 2021 | 44 |
| 2022 | 72 |
| 2023 | 35 |
| 2024 | 23 |
| Total | 5752 |