Ah, yes...but they are still quite sure where they were born! Regardless of evidence. ;-) Why? Well, because because people whom they feel they can trust (meaning their parents) told them where they were born, and that's what they go on, regardless of the presence (or not) of some apparently relevant official document saying where they were born.

An official document can be filled out in error. It can be a lie. It can be forged. Nothing else will convince a person of where they were born more than hearing about it from someone they personally trust...such as their Mom or Dad.

Since the birthers never knew Obama's Mom or Dad, all they really have to go on is various opinions that they hear from other people, and a birth certificate they've heard about also from other people. If they don't trust the people they've hear about it from, then they won't believe it. If they do believe the people they hear about it from who say that Obama wasn't born in America, then that's what they'll believe.

You see?

People believe what they wish to believe. This is true of almost all people almost all the time. Only when confronted with massive and irrefutable evidence to the contrary will they alter their favored set of beliefs.

Within their chosen set of beliefs, they are sentient and rational. But their sentience or at least their rationality stops dead at the barrier beyond which they are unwilling to go, and that barrier is the outer boundary of what they want to believe.

Watch a movie "The Downfall" about the last days in Hitler's bunker for a chilling demonstration of those dynamics at work in some highly intelligent people....but people hemmed in by strong political beliefs. Some of them eventually broke past the barriers of their own chosen beliefs and saw the reality of the situation. Others could not do so, and they chose death instead.