True, there's no proof that Alston was hospitalized after his January 1969 wound -- but neither is there any proof that he returned to PCF-94 to serve with Kerry for "four months," as he states. He is not in the picture of the crew taken roughly a month after his injury.
The burden of proof is on the party who intends to claim that someone is lying! WE have to prove that he didn't return to Kerry's boat or we have to let it drop.