My grandmother was born in 1910 and did not obtain a "delayed" birth certificate until some time in the 1930's. In order to obtain her birth certificate she had to provide 2 forms of identification. Her identification was one of her son's birth certificates and the family bible, both documents listed her age. Her name and birth date wasn't placed in the family bible until well after her birth, and she was never sure whether she was born in 1910 or 1911 (according to census records found later, she was definitely born in 1910). So, the dates of birth may not always be accurate.