For example why is the UK given as 927? The Kingdom of Great Britain formed in 1707 via the Act of Union between England and Scotland, it became the United Kingdom of Great Britain and Ireland in 1800 and then renamed to the United Kingdom of Great Britain and Northern Ireland in 1927. Ireland is given a date of 1542 which links to the formation of the Kingdom of Ireland but this was in personal union with the English (and then British) crown, so it was not a sovereign entity.
The dates for Australia, Canada and New Zealand are inconsistent. For Australia and New Zealand the dates coincide with the dates of self-government. For Canada (excluding Newfoundland) the equivalent date would be 1867 not 1931. The 1931 Statue of Westminster in 1931 restricted the ability of the British parliament to legislate for each of these countries, but it was only in the 1980s that all remaining links to the British parliament were removed (1982 for Canada, and 1986 for Australia and New Zealand).