He doesn't have to. He has to show that Libby knew Plame's status "for a fact," because Libby called the CIA and asked - and then that Libby consciously withheld from investigators that he knew Plame's status "for a fact," having called the CIA and inquired.
Exactly what her status is isn't pertinent to the question of whether or not his answers to investigators were deliberate misdirection.
"Exactly what her status is isn't pertinent to the question of whether or not his answers to investigators were deliberate misdirection."
I agree. I just don't know what motive would be if he did not believe she was classifed.
It certainly would diminish his motive to do so.