For me, I can totally see Jack keeping it a secret. Jack would do ANYTHING for Nicky, even joining the army and going to Vietnam just to watch over him. I could see him keeping it a secret to protect him. I am just confused because if they (or even just Nick) did fake his death, he would have been on the "dead soldiers" memorial. The guide said Nick's name was not on the memorial so therefore, he did not die in the war. It just makes me wonder how and why they all thought he died. I thought Kevin said that his Uncle Nick died in the war, so that was the story Jack told. But since we know his is alive and that "officially" he is not listed as someone who died in the war, they must have made it up after the war?