Even though birth certificates started in Baltimore City
in 1875, they were not mandated until much later. My
paternal grandparents born in 1891 and their siblings did
not have birth ceritifcates, my maternal grandfather born
in 1899 also didn't have one but my maternal grandmother
born in 1906 did. They were all born in Baltimore City.
My grandparents who didn't have birth certificates used
baptismal records to prove their birth dates when getting
their Social Security Cards.
Oddly my grandmother who had a birth certificate didn't
have a copy of it until she needed it to start collecting
social security when she was 62. She ordered one from
Vital Records and found out her birthday was different
than she had been told by her parents; 1 day different.
My grandmother brushed it off and said she wasn't
changing it at her age. She even blamed her father who
completed the form as being the one who was wrong because
"my mother wouldn't have confused it". Needless to say
she hadn't been on good terms with her father ever.