MtnTABS,
Oh dear, it sounds like you did not file IRS 8606 forms in the past to keep track of the basis. According to part of the lengthy discussion in the article
https://ttlc.intuit.com/community/retirement/discussion/i-neglected-to-file-my-non-deductible-ira-co...
the IRS takes a position that any such contributions not reported on 8606 are not treated as basis in your IRA. If you did make nondeductible contributions in the last 3 years (maybe only 2 as it is past April 15), you can file the 8606 forms with the IRS and pay a $50 late fee for each of those 2-3 years you did make nondeductible contributions. (You can plead ignorance and ask the IRS to waive the fee.) Use the basis total reported on those late forms as your IRA basis for your 2019 amendment.
