If there is a * (asterisk) next to line 15 then the calculations were done on the "Taxable IRA Distribution Worksheet" instead of the 8606 lines 6-13. This worksheet is described in IRS Publication 590-B worksheet 1-1.
https://www.irs.gov/publications/p590b#en_US_2020_publink1000270091
**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.**
