if you sold covered shares the basis is reported to the IRS. You have to use that value unless you are going to claim it is wrong.
That leaves the un-covered shares.
the un-covered basis can be relied on if the broker supplies it.
the two figures should add to your total investment in the fund, including reinvested dividends, which is why you want to use the broker numbers. most people don't track reinvested dividends.
