You should have submitted a 2017 8606 form that reported the non-deductible contribution on line 1 and a 2018 8606 for that years contribution with the total on line 14. The total of all contributions (assuming no distributions) would be on line 14 of the last filed 8606 which is then used as your basis for the 2019 distribution/conversion.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
