The 2018 carry forward basis will be on the 2018 8606 line 14, not necessarily the same as lines 2 & 3. (The actual carry forward 2018 basis will be found on the 2018 "IRA Information Worksheet" line 3, that is where TurboTax get the value to transfer to 2019.)
When entering the 2019 1099-R that carry forward basis should auto populate the "enter non-deducible basis" from prior year. If you enter a different value then yiu can provide an explanation statement as to why it is different.
Note that if you amended 2018 and changed the basis, then only the original 2018 values import, you would need to manually change it and add the statement.
**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.**