How did you report the Roth conversion as nontaxable without filing Form 8606. All Roth conversions are required to be reported on Form 8606. Without Forms 8606 showing the calculation of the nontaxable and taxable amounts of your Roth conversions, it's odd that you haven't received any notices for the IRS claiming that you have underreported your taxable income.
I must leave it to you to decide whether or not to file the delinquent forms. The IRS will likely charge the advertised $50 penalty for each Form 8606 that you failed to file if they discover that you have failed to file these forms and end up using your Forms 1099-R, Forms 5498 and your tax returns to substantiate that the Roth conversions were nontaxable.
