I would assume then, that 1) they entered therapy for a compelling reason that didn't involve admitting to being a narcissist from the outset, and 2) they were not as far along the spectrum of narcissism as the "average" narcissist.
I'd love to be wrong and to see more than the occasional "the exception proves the rule" situation. The world needs to heal and to stop the gaslighting and the manipulation from continuing down the generations.