Other mistake: During the ending scene, when Samuel L. Jackson is walking away from the camera across the lawn, he passes directly between the platoon on the right practicing rifle drill, and the platoon leader giving them orders. Marines are taught to NEVER do this. It is called "breaking ranks", and a Colonel in the Marine Corps would have known this.
Other mistake: After the marines have fired at the crowd you get a passing shot of the dead women and children. As the shot passes a young dead girl you can see her hand is twitching from a buzzing fly.