The idea that an island of rouge pirates could have remained undetected during the 20th century is incredibly unrealistic. During the First and especially the Second World War, the Bahamas were extensively patrolled by both British and American forces out of fear that German U-boats would prey on the smaller shipping in the area or perhaps even use one of the islands as a staging base for attacks into the Gulf of Mexico. By the time of the 1970s, geological and cartographic surveys had mapped all of the Bahamas and nearly all of the islands had been visited by surveyors.
Just as Michael Caine exits the plane right before it explodes, he yells "Run, Jeffrey, run" to his son. But his son's name (the character) is Justin, not Jeffrey. Jeffrey is the first name of the actor who plays the son.