If you're in a monthslong relationship with a girl it seems there would be some, little, something, that you would know about her or her family that she would've relayed to you at some point through conversation, that if verified by family would help corroborate your story. An elementary example would be, the reason for her knee brace. More substantial would be her confiding in him some event in her life or some family dynamic that only those close to the family would know. Something not in the media. I see he's honed his talking points and is fairly well spoken so did anything like that happen? If he knew Stacy for months how well can he speak on her? Doesn't need to be her life story, a few verifiable, unreported nuggets of info would've sufficed.
He should have been able to prove a relationship of that length existed without relying solely on the word of his family. The 11th hour statement from the co-worker that came 23 years after the fact is not something to simply accept at face value.