*Excludes Observations that spanned multiple years
| Pre 1970 | 20 |
|---|---|
| 1970 | 56 |
| 1971 | 43 |
| 1972 | 69 |
| 1973 | 24 |
| 1974 | 8 |
| 1975 | 90 |
| 1976 | 147 |
| 1977 | 110 |
| 1978 | 54 |
| 1979 | 117 |
| 1980 | 297 |
| 1981 | 307 |
| 1982 | 346 |
| 1983 | 239 |
| 1984 | 227 |
| 1985 | 292 |
| 1986 | 47 |
| 1987 | 109 |
| 1988 | 39 |
| 1989 | 25 |
| 1990 | 30 |
| 1991 | 23 |
| 1992 | 34 |
| 1993 | 35 |
| 1994 | 12 |
| 1995 | 29 |
| 1996 | 33 |
| 1997 | 29 |
| 1998 | 47 |
| 1999 | 15 |
| 2000 | 28 |
| 2001 | 14 |
| 2002 | 25 |
| 2003 | 69 |
| 2004 | 30 |
| 2005 | 37 |
| 2006 | 19 |
| 2007 | 50 |
| 2008 | 107 |
| 2009 | 157 |
| 2010 | 163 |
| 2011 | 147 |
| 2012 | 136 |
| 2013 | 331 |
| 2014 | 51 |
| 2015 | 108 |
| 2016 | 75 |
| 2017 | 44 |
| 2018 | 48 |
| 2019 | 96 |
| 2020 | 37 |
| 2021 | 17 |
| 2022 | 26 |
| 2023 | 2 |
| Total | 4770 |