Fuchs' example of Czechoslovakia made me think of the Polish forces' surrender in 1939. I think Poland as a nation never officially surrendered. In 1940, France, as I remember the case, did not actually surrender either. An armistice was signed by General Huntziger, perhaps on behalf of the French Government, but no peace treaty was ever signed.

So perhaps a first step in the process would be to decide what counts as surrender. I think we have a fairly clear case of what that means when military forces surrender--they lay down arms and agree to stop fighting as an armed force, usually for a specified period of time.

Nations, on the other hand, do not surrender in the same way. I submit the people of the occupied parts of the the nation either acquiesce in the process of being absorbed by their conquerors (or at least being detached from the rule of their former government) or accept their government's agreement not to do whatever it was that caused their opponents to start fighting with them in the first place. I am not sure that this would be surrender in the same sense that an army surrenders though. Just as the "contracts" by which governments are established/receive their legitimacy seem to be somewhat mythical, I think national surrenders as datable events are equally chimerical.