1801 - 1900 (19th Century, 4th edition).

1901 - Present (2004, 31st edition).

1901 - 2000 (2009, 36th edition).

1901 - 2000 (2014, 41st edition).

1901 - 2000 (2017, 44th edition).

2001 - Date (2009, 3rd edition).

2001 - Date (2011, 5th edition).

2001 - Date (2014, 8th edition).

2001 - Date (2017, 11th edition).