During the Vietnam War, those who were prisoners at the hands of the Vietcong were moved quite often to avoid being located by US forces, just like as it happens during the second Rambo movie.
During the Vietnam War none of the long-before-planned rescue raids ever freed any American prisoner of war. And this was due to the presence of a mole right inside the macVsog, which used to warn the Vietcong before any raids took place.
Here below: at the end of a rescue mission, soldiers examine some cages that were filled with US POWs until some minutes before their attack.
There is a scene in the movie during which Rambo arrives at the camp and he 'shouldn't find any POWs at all': this scene painfully remembers something that actually happened too many times during the Vietnam War
The mole inside the MacVsog was never found and after many failed attempts, many started to think it was the CIA brass heads – or the US government itself - that used to sabotage any POW rescue attempt for unknown reasons at the time.
The Rambo II plot revolves around these themes, creating a confusing mix of reality and fiction.