On or after the 6 April 1950 is the key birth date.
Bizarre when one thinks about it. Whilst the date of retirement for women moves progressively out to age 65 over several years, the date at which the ENTITLEMENT to a full pension moves from 39 yrs to 30 yrs contribution at the stroke of one day. I guess Government will say that there has been 10+ yrs warning of this / many working women retiring have the 39yrs of contributions anyway.
Sorry, I don't know the answer to your original question.