Corrected entry: After Jacob's harrowing experience in the subway at the beginning, we get an establishing shot of the New York skyline which includes the World Trade Center. The Trade Center was not completed until 1973--the same year the Vietnam War ended. Jacob would have been stabbed and died before it was there.
Corrected entry: In the opening scene we are told that we are looking at the Mekong Delta in Vietnam. A few moments later, a soldier appears wearing a 1st Division patch on his shoulder. The 1st Division was never in the Delta (they were in the Northern Highlands).
Correction: It's possible the soldier was transferred from the 1st and hadn't changed his patch yet or wasn't planning to change it at all. Uniform regulations during Vietnam were far more lax than today.
Correction: The scene is supposed to be based years after Jacobs serving in Vietnam, thereby making the World Trade Center complete.