Hey Kevmo. There are other possibilities. They may list his religion, he may have had a different birth name, his parents may not have been married, etc
Barack's mother may not know who the father was.
I think it's gone beyond that. Things have reached a point where this BC thing is becoming the issue: what's he hiding, what's it say, where wouldn't he release it, why haven't..., why aren't..., what's with... etc.
Unless this BC turns out to be as pure as mother's-milk there's going to be ^%*## to pay. B/c then comes to question: "If this is legit, why did he take so long to release it?"
According to what I have read, his parents were not "legally" married as his father was still married to his first wife (who was in Kenya) when he married Obama's mother. However, that isn't really relevant to the question of his eligibility.
Actually, I don't believe his parents were legally married. Obama Sr. still had a wife in Africa (and children too).