If I should start a new post just let me know. But my situation is very similar. I had non-deductible contributions 2 years only.
In 2009 I filed form 8606. No problem.
In 2010 I filed form 8606, but neglected to list and add the basis from the 2009 form. I used TurboTax both years, so I'm not sure why TT didn't bring it forward automatically. A bug perhaps?
Now in 2019 I've taken my first ever distribution from a traditional IRA (a rollover IRA that used to be my 401k), so I need my correct basis. I assume that I need to file an amended 8606 for 2010 (using that year's form) and a letter of explanation. I am hoping that nothing more will come of it. Financially it doesn't make sense to pay penalties to recover the basis from 2009 - it's a small enough amount that paying taxes on that amount again would probably be cheaper than a penalty.
My first question then is, if I file an amended 8606, can I expect to get a free pass, or a fine? And if it's a fine, can I just use the (too small) basis from the 2010 form without getting a fine?