[CHY872]

This sort of thing leads to finicky rulings everywhere, though. For example, if I build an airport, I probably will have to compulsorily purchase a bunch of land from people and demolish their homes. I must purchase the land at the market price (at least according to UK law) so that they are left in the same financial position after the purchase.

Now say that 50 years later, its realised that there's a whole load of diamonds under the airport (not known to anyone). Clearly, we would not compensate the original owners.

The only difference here is that the people who owned the land were not compensated for it. Those people are now mostly dead or nearly dead.