My grandmother "altered" her date of birth on her birth certificate so her husband wouldn't know she was older than he was. That date ended up on their marriag

My grandmother "altered" her date of birth on her birth certificate so her husband wouldn't know she was older than he was. That date ended up on their marriage certificate. And then, after her husband passed away and she was approaching pension age, she realised she would only be eligible for the pension a few years later... So DOB is not immutable. (and another common source of DOB errors, mixing up the US MM-DD-YYYY versus the normal DD-MM-YYYY format used almost everywhere else...)