The UK allows for retrospective overseas birth registrations.

The UK also allows for retrospective legitimisation if the parents marry after the birth of the child.

The UK however has a cap on the date for such processes which means that if the person was born before 1985 overseas, they cannot get full legitimacy even though they are entitled to this under the Legitimacy Act 1976 which states: 

Subject to the following provisions of this Act, where the Mother and Father of an illegitimate person marry one another, the marriage shall, if the father of the illegitimate person is at the date of marriage domiciled in England and Wales, render that person, if living, legitimate from that date.

For Commonwealth Overseas Foreign Birth registrations this is not possible due to the restriction of date on this process, namely you can only do this if the child was born on or after 1 January 1983.  This creates an injustice based on age and those born in commonwealth countries should be given the right to legitimacy and the change of their Birth certificate to include their Father and the subsequent Marriage.