Electronic money, Stock etc are defined as Fungible because two people can exchange tokens of ownership in the same thing without impacting anything. The same is 'said' about crude oil and other physical thing even though they are not actually identical they are treated as such.

However, the same effect happens when company's own huge set's of IP. That IP is treated as an income stream and money does not care about it's origin. The reverse even happens with money. Coins as collectors items are independent from there nominal value.

For a back and forth example. Two Kids might trade 1's because the Serial Numbers of one of the bills contain 666 which lowers the value to one and increases it to another. Later if the bill is spent it could go though a hundred transactions where nobody cares about the SN.