There is a recent question on Skeptics SE concerning the peace treaty between Germany and the allied powers, the validity of the German constitution, and consequently the existence of the Federal Republic of Germany. Together with the excellent juridical answers there, I think the most important argument for the legality of modern day Germany is that >99% of Germans are living happily in the FRG and also the country's tight integration in the UN, EU, NATO, OSCE and other international organizations.
However, international treaties are complex, so let's imagine there is really some flaw in one of the underlying contracts (say some technicality like a missing signature in the small print or whatever). What would be the consequences, particularly in the light of recently cooling relationships with three of the four allied powers? Could there simply apply some sort of common law of international politics and the missing signature would silently be added by the next occasion? And finally, is there any precedent for such a case?