Are they really different? You can sell a single car, or a yard full of cars, but I accept the restriction as a result of division. Maybe I should have said Satoshi instead of Bitcoin. Every Bitcoin transaction is recorded permanently ( I don't include transactions inside an exchange), and it has an acquisition and disposal value.
Let's go with Satoshis.
You have bought once 1000 sats and once 1000 satoshis. You move them both to the same address you have different outputs but the same balance. Then you decide to spend 500 satoshis, from which batch have you spent those satoshis? When you have two packed cars in a garage you for sure know which one you have sold, right?
Do you really think the IRS will waste time trying to figure out this kind of thing?
I wonder if anyone has put this situation to a revenue department. Bitcoin is unlike any of the other assets that they have had to consider. I suspect if you submitted a return based on transaction IDs, then they would accept it, rather than go down another rabbit hole.
Nobody in the IRS is going to care about the transactions ID, what they are going to care about is the proof you have paid x for them, the statement from the bank or the exchange or whatever means you have used to purchase those coins.
Especially since in the UK it's clear they use share pooling I advise you to speak with a tax expert before you go out and do something you might regret based on what you think it's right.
