Retirement tax questions
Go back and fill one out for each year and mail each one in separately. You can go back and use software or just fill it out by hand. You need the form and instructions. You will need to print the correct year for each one. You can go as far back as necessary. It is better to do it now rather than when the IRS asks later.
See:
About Form 8606, Nondeductible IRAs
For prior years, search the IRS here
