Only 4 people ever knew the identity of "Deep throat" and all 4 of them are saying its this guy.
If its not, there will never be a way to prove it was somone else, and if it is, everyone who is a source is agreeing.
I find it hard to believe that ONLY 4 people knew. Who could sit on that information for all these years?
Anyway how can it be proven one way or the other? We just have to say ok and move on I guess.