I'll assume you are talking about the Nordyke certs? You do realize that the Nordyke certs were requested and issued in 1966, right? And that Obama's was just done, in 2011? So of course the Registrar is a different person. And perhaps they don't have the Director of Health sign it any more. A lot can change in 50 years.
The registrar, the doctor and the parent are all put on there at birth. The ONLY thing that would be different from year to year is the signature of the one who signed and stamped the certificate certifying that it is a certified copy requested in that particular year. A registrar in 2001 can not certify ANYTHING about a birth even 10 years ago - only on the date of the child.