After 12-hours elapsed and I did not receive a response to my initial inquiry seeking an "elegant" way to recover following my realization (far along into my 2025 return) that I'd somehow overlooked the nondeductable IRA basis tracking step when using TurboTax to prepare my 2024 return a year ago, I did decide to go ahead and update my almost-finished 2025 return this way ---
``I realize that I can go to the Forms list and pull-up the 8606-T and 8606-S forms in the current (2025) return in progress using TurboTax 2025 Desktop, then manually over-write the incorrect nondeductable IRA basis totals... '' [i.e., the amounts from 2024 that are used as the starting points for the calculation of the new totals to be reported for 2025, following any new nondeductable IRA contributions within the tax year of the current tax return being prepared].
"Over-write" = the "override" option -- but clicking on the prior year's nondeductable basis in the Form 8606 did a quick-zoom to where that same number appears in a linked worksheet, and inside the worksheet it was not necessary to actually override the old value ... instead I was simply able to enter the correct value, which was accepted and auto-populated the value in the Form 8606.
Hopefully others in similar situations find this helpful.
-- Jim
P.S. A reminder question during FINAL REVIEW along the lines of ....
"In last year's return you had a nondeductable IRA basis total tracked via Form 8606, but in reviewing your return for this year, TurboTax finds no Form 8606 present to continue tracking your nondeductable IRA basis total (including any additional nondeductable IRA contribution(s) you may have made since last year's return was submitted). Do you want to include Form 8606 in this return ? YES / NO"
Had this been a "feature" of TurboTax back in 2024 (and today), it might have helped me (and by extension maybe also some of your current+future customers) catch oversight(s) like the one I made last year --- thereby avoiding the need to file a 1040-X after-the-fact to remedy such oversight(s), as well as eliminate the particular problem I was facing when I posted here for help, namely how to get the amended 1040-X numbers into my tax-return-in-progress using TurboTax ....
Please consider the pros/cons of checking for missing nondeductable IRA contributions during FINAL REVIEW for taxpayers who made such contributions on their previous return but have not provided analogous input on the current tax-return-in-progress, in order to double-check if zero contribution this time around was intentional (correct) as opposed to an accidental oversight (incorrect).
Even in the absence of NEW nondeductable IRA contributions made during the tax year within scope of the current return, I am also both surprised and disappointed to have discovered that "carry over" 8606 Forms are not generated automatically by TurboTax as part of the "Save For Your Records" set of tax documents. Not everyone is fastidious when it comes to keeping & maintaining accurate financial records, so TurboTax would be doing customers a favor [and a potentially financially-valuable favor at that] by including such cumulative dollar amounts (such as nondeductable IRA basis amounts) up-to-date from year-to-year in the "Save For Your Records" set of tax documents whenever TurboTax is cognizant of any such contributions having been made in the past, whether or not any new analogous contributions were entered in the course of preparing this year's return. "Save For Your Records" printed-copies or PDFs that spouses and/or caregiving/assisting adult children can access among an elder's financial records outside of TurboTax could be very beneficial, versus potentially "losing track" of any nondeductable basis in an elder's IRA.
