I'm pretty sure they have the Coinbase's database and would not be able to trace holders that are using non-KYC exchanges and services
also they are stating that purchasing ( and therefore holding ) bitcoin is not a taxable event, but :
"paying with the cryptocurrency to buy something else is a sale of Bitcoin, similar to the sale of a property. Therefore, it is a taxable event"
so they expect you to pay taxes every time you sell bitcoins , but how on Earth can they prove that your transaction was sales , bar having information from certain exchanges and services
therefore if you live in the US , get ready to pay your taxes on bitcoin transactions and have lovely time proving that the 0.8 btc transfer from your cold storage wasn't sales
or do not use government controlled exchanges and leave your personal data to any KYC compliant companies
This is great explanation, how to trace the real crypto holders to pay taxes, even if the exchange(coinbase) have an kyc requiremments to their users impossible to trace the real holders some holders are using fake indentification to submit as kyc requiremments, so it's is very difficult from the U.S irs to collect taxes came from the data of coinbase.