I really appreciate your help and insight. After experimenting a bit, it looks to me like - as you say - the purpose of characterizing the 401k Rollover to a Rollover Roth IRA is only to track this as the Roth IRA Basis on the TT "IRA Information Worksheet." Instead of changing my 2023 1099s, I will wait for 2024 tax reporting and then enter the correct Basis for the Roth account.
In the Deductions section I was prompted to input the correct after-tax Basis for my Traditional IRA account this year (a Basis that has not changed since 2008) and when, as an experiment, I entered a Roth IRA Basis for a year prior to 2023 TT correctly displayed it as the Basis on the IRA Information Worksheet...the same as if I had split my original 2023 1099-R document into two separate 1099s (one with all proceeds to a Roth IRA and one not).
It's a little inconvenient, but I prefer to enter my 1099s exactly as I received them, and I will establish the correct Basis for the Roth account, which will not affect my tax reporting this year but may simplify future tracking in TurboTax, next year. But again....THANK YOU for your help!!
