@macuser_22, thanks for your reply. I tried editing the existing 1099-R from exactly the location in TTax that you specify. However, I didn't get asked the question about nondeductible contributions under discussion (though I remember seeing it before when entering 1099-R data).
All of the withdrawal went to QCDs, and the total withdrawn exceeded the RMD from that IRA. Could that have anything to do with the fact that the question about nondeductible contributions isn't asked?
As I wrote initially, I also tried creating another version of the 1099-R for the IRA with basis from the same location of the TTax interview, and still I didn't get the question.
Incidentally, isn't it true that if I had satisfied the total of all the RMDs required (based on their 12/31/18 balances and my age) with withdrawals from other IRAs which contain no bases, the IRS imputes a fraction of that total is return of nondeductible contributions not to be taxed? If so, then correctly answering the nondeductible contributions question for each IRA would not produce the correct result, namely that the basis of an IRA from which there was no withdrawal is nonetheless decreased.
