*Excludes Observations that spanned multiple years
| Pre 1970 | 115 |
|---|---|
| 1970 | 8 |
| 1971 | 15 |
| 1972 | 14 |
| 1973 | 10 |
| 1974 | 17 |
| 1975 | 11 |
| 1976 | 21 |
| 1977 | 20 |
| 1978 | 6 |
| 1979 | 35 |
| 1980 | 62 |
| 1981 | 45 |
| 1982 | 30 |
| 1983 | 13 |
| 1984 | 21 |
| 1985 | 12 |
| 1986 | 8 |
| 1987 | 6 |
| 1988 | 25 |
| 1989 | 34 |
| 1990 | 32 |
| 1991 | 41 |
| 1992 | 26 |
| 1993 | 88 |
| 1994 | 77 |
| 1995 | 67 |
| 1996 | 50 |
| 1997 | 60 |
| 1998 | 53 |
| 1999 | 65 |
| 2000 | 102 |
| 2001 | 107 |
| 2002 | 149 |
| 2003 | 69 |
| 2004 | 51 |
| 2005 | 46 |
| 2006 | 62 |
| 2007 | 72 |
| 2008 | 102 |
| 2009 | 116 |
| 2010 | 103 |
| 2011 | 95 |
| 2012 | 87 |
| 2013 | 344 |
| 2014 | 119 |
| 2015 | 91 |
| 2016 | 79 |
| 2017 | 30 |
| 2018 | 23 |
| 2019 | 29 |
| 2020 | 26 |
| 2021 | 28 |
| 2022 | 18 |
| 2023 | 14 |
| 2024 | 11 |
| Total | 3060 |