A lot of people hadn’t really studied the issue very well in 2008, nevertheless, the Supreme Court rulings are consistnt in defining NBC as a person born in the country to a citizen father (or citizen parents).
According to dozens of people I've spoken to, everyone above a certain age was taught in civics class that NBC meant having two citizen parents.
Depending on the argument, it was either well-known or not known at all until Obama took office.