Any time they are carrying their rifles, Danny Glover and the others carry properly with their finger extended off the trigger. Ray Liotta constantly has his finger on the trigger. Against all rules of gun safety.
In the cast listing David Poole(Dennis Leary) is listed as Lt. Poole. In the movie he is actually a US Army Chief Warrant Officer Three. This can be seen by the right collar bar on his uniform that has a bar with three black boxes and by the Warrant officer insignia on the left collar.
During the negotiations to buy Bo-Tat the insignia on Doyle's beret is reversed. The insignia is of the 5th Special Forces Group and is a diagonal yellow stripe with three scarlet stripes in it going from the top left (as seen by the observer) to the lower right.) Doyle's is going top right to lower left. (NOTE: It happens that the Vietnamese flag is yellow with three horizontal red stripes.)
When BoTat and the Soldiers come under fire boating down the river, if you watch carefully, one of the mortar rounds can be seen bouncing partially out of the mortar pipe on deck the VC boat and falling back in instead of being fired out like it should.