Theoretically, the Internal Revenue Service (IRS) could look through every transaction on every blockchain to see profits and losses in each wallet or account. From there, the IRS could figure out the amount of on-chain gains it could tax. However, that raises the issue of whether those assets were sent from one wallet to another with the same owner, something that may not make it a taxable event. On top of that, there’s the difficulty of getting good information from exchanges to figure out the amount of off-chain gains the IRS could tax. In practice, this collection and estimation process is a mess.