it is your responsibility to review the import for correctness. sometimes the broker does not have all the info or is otherwise unable to supply the correct amounts. the most common situations are when securities are transferred from another broker. the new broker may use the market value on the date of the transfer rather than your actual cost basis. another would be wash sales when you have multiple accounts taxable or nontaxable. for example, selling a security at a loss in a taxable account and within the wash sale period acquiring substantial identical securities in a nontaxable account.
these are rare but do happen.
