Legal Question in Family Law in California

There are some exceptions based on the passage of time without doing anything to claim he is the father, but if he files a request for a paternity determination within a reasonable time of knowing he may be a father, the court will almost invariably order DNA testing and will make a conclusive determination of who the father is. The one big exception is if the mother was married to and in conjugal cohabitation with the father named on the birth certificate. In that case there is a conclusive presumption that the husband/father is the true father.

You need to speak to a family law attorney who is thoroughly familiar with California's quirky paternity law. The birth certificate is not so much important as other issues, such as marriage, whether someone signed a voluntary declaration of paternity, and the amount of time that has passed since the birth of the child.