Since I've already stated my opinion earlier, I can safely play devils advocate on this.
Gunslinger, speaking hypothetically, apply the concept of receiving stolen property to this. If a car is stolen, then sold to an innocent third party, when the auto is identified, who gets to keep it? The original owner? Or the third party? In the US, the law has established that the innocent 3rd party has no property rights. Possibly, they might be able to pursue legal reparation from the party that sold the hot car to them, but that's a separate matter. If we applied that same model to this, then the couple that bought the land on the beach would need to take up that conversation with the US Government or Dole corporation, right?