A few points:
Sam are you talking about an autobiography here? It may make a difference.
The ‘hour away’ = 30 miles is just your supposition. Moreover, reading the phrase ‘hour away’ I imagine it is used casually. It might denote a variety of things. Even considering that, I think 30 miles is at the upper limit of plausibility.
Consider if, as you claim, the border was heavily patrolled. In that case I would think an hour’s travel by boat would amount to less than 5 mi.
Is it a lie, though? Well, why would he bother? I just cannot see the leverage in alleging he was shot at from one side of a border rather than another.
I mean we know troops were in C, so what’s the difference? I think if there is an acknowledgment that formal operations began in 1970, it is certain those operations followed on a history of informal incursions. These things are never so neat.
How Kerry is Campaigning? It’s a tough game, I fully expect him to fight hard and aggressive. Whether there is substance or not, especially if there is substance why go on the back foot and allow this to become an issue by giving it life and debate.
If you expect this to become an issue, my guess is disappointment awaits. Trivial, inconsequential and ultimately indeterminable.