> I guess shares are supposed to be fungible but in some way they are not exactly - if the company has a share register, and shares are numbered then what number does Mr C get?
Currency is also numbered. If I lend you $20, it's not fraud to give me a $20 back with a different serial number on it. It's not even fraud to give me back two $10s. Adding those kinds of restrictions would defeat much of the point of lending you $20 in the first place. It's also not fraud to spend it at Mr C's eatery for lunch, and hope you can replace it later - in fact, that's the whole point of borrowing money.
Currency is also numbered. If I lend you $20, it's not fraud to give me a $20 back with a different serial number on it. It's not even fraud to give me back two $10s. Adding those kinds of restrictions would defeat much of the point of lending you $20 in the first place. It's also not fraud to spend it at Mr C's eatery for lunch, and hope you can replace it later - in fact, that's the whole point of borrowing money.