Let me put this simply--and I suggest you reread the article for details==Alston was removed from the boat and medevaced out for treatment of a shrapnel inflicted head would on January 29th--Kerry assumed command of that boat on January 30. Alston mother stated he returned home after he was wounded. Under those circumstances and others detailed in the article, it is unlikely that Alston served on that boat under Kerry.
I've read the articles, but I'm more of a skimmer. I guess I missed the one where his mom said that he returned home. Perhaps you could guide me too it.
Also, you use the word "likely", which is more in keeping with the story than Stayout's post 27 saying this proved that Alston was not on Kerry's crew.