I could be wrong, but isn't it true that once the Supreme Court has ruled, a precedent is set, and lower courts are bound to rule in accordance with that precedent? If a lower court decides in conflict with a Supreme Court ruling, than can't the lower courts decision be overturned?
Sure, and they *usually* are. But every case has a slightly different set of circumstances, and the later Supreme Court may decide that their earlier decision does not apply to the circumstances of the new case.
However, the Supreme Court has never decided a case based on the definition of Natural Born Citizen. It's been mentioned in dicta, but no case has turned on the meaning of the term. This is not suprising, since the only place it is in the Constitution is in the clause which provides the requirements for someone to be eligible to the office of President. No where in the statute law is one required to be a Natural Born Citizen to be eligible for something or to have some privilege or immunity. No law explicitly makes one a Natural Born Citizen, and the statute laws which make people born outside the country citizens at birth (subject various criteria), are enacted under the power to define rules of Naturalization. The courts have ruled that, for Constitutional purposes, those citizens are naturalized.