Good news! I was able to work through this using ChatGPT.
Turns out that total prior year(s) depreciation of a sold vehicle cannot exceed the business use % of the vehicle for the FIRST year it was placed in service.
TurboTax, and any of the community forum topics here, did not explain this clearly, nor help me to determine what that was - I had to go to OpenAI to get the correct answers.
In fact, TurboTax software directly led me on the wrong path to complete my taxes this year, asking me instead to calculate depreciation for all prior years and aggregate it.
