I always thought that if a child is born out of wedlock, the baby automatically carries its mother’s maiden last name (while his middle name is left blank, otherwise, the baby and the mom will appear to be siblings). Only when the baby’s parents marry will the child have the legal right to adopt the father’s last name.
Apparently, this is not always the case. Some children are able to carry their father’s last name on their birth certificate even if their parents are not yet married.
How is this possible?