I believe this is the reason. I know that in some states the race of a Bi-racial child is listed as the mother’s race. Alabama is one.
I considered this potential at first as well but in all the birth certificates I have seen from the 60’s there are only race entries for mother and father. The child in question is essentially defined by the race of the parents.
But if w4women’s statement that Obama Sr. was not on the original BC would by default mean that Obama Jr. is considered caucasian by birth due to his mother’s race.
Why does it matter what race is shown on his birth certificate? It is easy to see he is part black by looking at him.