Trivia: Not really a mistake, given the need to maintain the story arc in the first half of the film, but in real life, Pyle would have been discharged from the Marine Corps within days of his starting basic training - for his own good. It happens all the time - dropout rate of boot camp recruits varies but is generally around 10%.
Trivia: When Jim returns home after losing his parents, his nanny slaps him. The actors had practiced a fake slap and fake reaction, but Spielberg and the actress playing the nanny conspired to make the slap real when the cameras were rolling, so Christian Bale's reaction would be genuine. Therefore, Bale is really being slapped, and his shocked reaction is no act.
Trivia: This film is based on Pentagon lawyer Adrian Cronauer's life as a DJ during the Vietnam War. He is worked in the Pentagon in its MIA/POW office until his death on July 18, 2018.