That's not exactly true. Kerry's story of spending Christmas in Cambodia has been retracted by his biographer, Douglas Brinkley. There's some research that suggests that Alston did not serve on Kerry's boat for long at all (about one week is the current best guess) and apparently not at the time that Alston received his serious wounds.

I think that it's important to separate truth from fiction and to understand what may not be proveable by either side, given the time that has elapsed since the events occurred.