| 1981 | B |
| 1982 | C |
| 1983 | D |
| 1984 | E |
| 1985 | F |
| 1986 | G |
| 1987 | H |
| 1988 | J |
| 1989 | K |
| 1990 | L |
| 1991 | M |
| 1992 | N |
| 1993 | P |
| 1994 | R |
| 1995 | S |
| 1996 | T |
| 1997 | V |
| 1998 | W |
| 1999 | X |
| 2000 | Y |
| 2001 | 1 |
| 2002 | 2 |
| 2003 | 3 |
| 2004 | 4 |
| 2005 | 5 |
| 2006 | 6 |
| 2007 | 7 |
| 2008 | 8 |
| 2009 | 9 |
| 2010 | A |
| 2011 | B |
| 2012 | C |
| 2013 | D |
| 2014 | E |
| 2015 | F |
| 2016 | G |
| 2017 | H |
| 2018 | J |
| 2019 | K |
| 2020 | L |
| 2021 | M |
| 2022 | N |
| 2023 | P |
| 2024 | R |
| 2025 | S |
| 2026 | T |
| 2027 | V |