Adoption paperwork

I recently found out I'm a birthfather. My son is an adult now, but during my search I think I have found him via several search programs, the internet, police software, and a witness that knows him. It appears as if he had been adopted at some point. The only problem that makes me not 100% sure I have found him is that his birthday does not match his original birthday. Is it possible (not neccessarily legal) to have a birthday changed as well as the last name during the adoption process in the state of California? His birthmother will not cooperate with me and help me find him. Thanks for any help you can offer with this problem.