[aristus]

Of course they are numbered, just like any $1 bill. They are not registered as far as I can tell; they are bearer bonds (just like a $1 bill).

Now say you have several trillion dollars outstanding to many people who are not quite your friends, nor very interested in rummaging through their books to help you, revealing their hands in a very high-stakes game. Then some other government turns up a ridiculous amount of bonds designed to be anonymous (just like a... you get the picture). Also, a third government has some claim because it crossed her border.

That is a classic "international incident". It will take some time to resolve. Lots of favors will be traded. Joe Public may never know the details.