My father was born at home in 1912. He lived to be 95 and never had a birth certificate until he was 65 and needed one for SS. Both his parents were deceased so he had an Aunt who filled out an affidavit swearing to all the information to the best of her knowledge and then he was issued a "Delayed Birth Certificate."
Same with my mom, older sisters signed for her. BO has no one at this time to provide the secondary source in this manner...maybe a baptismal certificate or the family Bible /sarc