Re: Did Kirk captain any ship before Enterprise?
Again, nobody said anything about "irrefutable proof." We're just talking about evidence. There is one piece of weak evidence that Kirk had a prior command, and absolutely nothing to suggest he didn't. So that tips the scales at least slightly toward "yes." Even a little evidence outweighs zero evidence -- especially when there's no way of gathering any further canonical evidence that might alter the balance.
STAR TREK: 1964-1991, 2013-?