Capital gains tax basis for pre-immigration assets is nearly impossible to establish with IRS-acceptable documentation

When an immigrant becomes a US tax resident, their pre-existing investment portfolio's cost basis for US tax purposes should theoretically be the fair market value on the date they become a tax resident. But the IRS provides almost no guidance on how to establish and document this 'step-up' in basis. So what? When the immigrant eventually sells those assets, they need to prove their cost basis to avoid being taxed on gains that accrued entirely before they were a US tax resident. So what? Foreign brokerage statements may be in a different language, use different accounting standards, or not report cost basis at all (many countries don't track cost basis the way the US does). So what? Without clear documentation, CPAs often advise using zero as the cost basis, meaning the immigrant pays US capital gains tax on the ENTIRE sale price, not just gains accrued after becoming a US resident. So what? On a portfolio worth $200,000 at immigration that's now worth $250,000, the immigrant might pay tax on $250,000 of 'gains' instead of the actual $50,000 gain -- overpaying by approximately $30,000 in federal tax alone. So what? This amounts to a hidden tax on the act of immigrating to the United States, punishing people for having saved and invested responsibly before arriving. The problem persists because the IRS has never issued clear regulations or a standardized form for establishing pre-immigration cost basis. Revenue Ruling 64-44 provides some framework but is from 1964 and doesn't address modern securities. CPAs are left to use 'reasonable' documentation, which creates audit risk and inconsistency.