Hi

My wife and I have been making non-deductible traditional IRA contributions since 2007.

I did my taxes with Turbo Tax for many years and neglected to put those in (I thought it was just offering to record-keep for me, not that it was necessary for the return. Kind of like when it offers to prepare your estimated tax forms for the coming year).

Then I switched software and started entering the contributions a few years ago.

We are now considering conversion to a Roth.

I see now that there is an inaccurate cost basis on the Form 8606 that was submitted with our 2020 return. It's much too low.

What to do now? Do all those years of returns need to be amended? Or just a single amendment with the correct cost basis?

We haven't recharacterized anything yet, and may not, so no taxation has been impacted by my reporting error.

Thanks for your thoughts.