You can file amended tax returns to recoup some of the taxes you overpaid. Underreporting your cost basis will definitely create a situation of over taxation. See below for instructions for amending your returns in TurboTax. Please note, you can only go back three years from the due date of the return when filing amended returns for additional refunds. So, you have until April 15, 2020, to file an amendment for your 2016 tax return.
How to Amend
