I was subjected to backup withholding on an investment account. The 2013 form 1099-B indicated that there were transactions that cost basis could not be determined. I filed my 2013 tax without the form 8949 because I could not determine the cost basis at that time. I managed to trace back the cost basis recently. Hence my questions are:
1. How can I file the cost basis for the undetermined transactions now after I have already received my 2013 tax return?
2. Since I was subject to both federal and state withholding, how did the IRS calculate my tax return for undetermined-term transactions without 8949?
3. I may have missed entering my withholding tax during the filing as well, how can I make amendment for it now?
thanks,