| W1 | Wave 1 September 1999 - March 2000 |
| W2 | Wave 2 September 2000 - March 2001 |
| W3 | Wave 3 September 2001 - March 2002 |
| W4 | Wave 4 September 2002 - March 2003 |
| W5 | Wave 5 September 2003 - March 2004 |
| W6 | Wave 6 September 2004 - March 2005 |
| W7 | Wave 7 September 2005 - March 2006 |
| W8 | Wave 8 September 2006 - March 2007 |
| W9 | Wave 9 September 2007 - March 2008 |
| W10 | Wave 10 September 2008 - March 2009 |
| W11 | Wave 11 September 2009 - March 2010 |
| W12 | Wave 12 September 2010 - February 2011 |
| W13 | Wave 13 September 2011 - February 2012 |
| W14 | Wave 14 September 2012 - February 2013 |
| W15 | Wave 15 September 2013 - February 2014 |
| W16 | Wave 16 September 2014 - February 2015 |
| W17 | Wave 17 September 2015 - February 2016 |
| W18 | Wave 18 September 2016 - February 2017 |
| W19 | Wave 19 September 2017 - February 2018 |
| W20 | Wave 20 September 2018 - February 2019 |
| W21 | Wave 21 September 2019 - February 2020 |
| W22 | Wave 22 September 2020 - February 2021 |
| W23 | Wave 23 September 2021 - February 2022 |
| W24 | Wave 24 September 2022 - February 2023 |
| W25 | Wave 25 September 2023 - February 2024 |
| W26 | |