After selling a mutual fund held since 1993, I received my 1099-B with two parts. The second part stated " Transactions for which basis is NOT reported to the IRS and for which short-term or long-term determination is unknown. You must determine short-term or long-term gain/loss based on your records on Form 8949, Part I with Box B checked or on Form 8949 , Part II with Box E checked as appropriate". So , does that mean my cost basis is what I paid back in 1993 ( I never added any additional funds, reinvestments were from Capital Gains and Dividends).
