Presumptions can be overcome. If the defense makes offers a defense that the order is unlawful because Obama is not a legitimate President, the burden would then shift to the government since it has access or can get access to the appropriate documents.
That said, I am not going to be surprised if the judge or government refuses to turn over those documents. On the other hand, the members of the court martial board can choose to acquit if those documents are not provided to the defense no matter what the judge tells them.
I can’t speak for an actual legal strategy, but it seems to me that we’re looking at a form of civil disobedience aimed at defending the Constitution from a domestic threat (an illegal CinC). Is this deployment not part of Obama’s Afghanistan surge ... to me, there would be ways to connect these dots and justify civil disobedience.
I'm sorry again, but that's not even remotely true. You don't understand how the process works.