Character mistake: Tom states that the Republic of China released fifteen American POWs in 1955. The People's Republic of China (Communist China) might have done so, but the Republic of China (Taiwan) has always been an American ally and would not have been holding any Americans prisoner to begin with.
Factual error: In one scene Gunny watches King Kong (1933) and is terrified by a scene in which Kong munches on one of the natives. That scene was deleted from the original theatrical release and not restored until the 1970s, so he couldn't watch it in 1955.
Factual error: In the movie, orange reflector squares are on the highway between the broken yellow painted lines. Those weren't used on the 2 lane highways until the early '80s.
Factual error: When Jack is sunbathing in the backyard and is spotted by the lady neighbor, there is a shot with a plastic septic tank in the background. Back then septic tanks were made of concrete.
Factual error: Set in 1955, Tom Holman enters a construction site with an orange warning sign. Prior to 1971, construction signs were yellow.