MDM, do you have a plan for handling changes to state taxes by year with the sheet?
Good question! Now that one can select different years for federal returns by changing cell Calculations!R2 (currently 2021, 2022, or 2023) that does leave the questions of state taxes.
Historically I wait for the Tax Foundation's
State Individual Income Tax Rates and Brackets update, usually in February, and with a little reformatting that provides the update to the 'State Brackets' tab. Presumably the 2023 NC rate will be updated then.
Currently there is no plan to allow the same choice of state tax year as there is for the federal tax year. Although (and thanks in no small part to feedback from yourself and others) I believe the federal calculations to be extremely accurate, in general there isn't nearly the same effort expended for state calculations. Even so, most if not all of the state calculations are "reasonably accurate" (or at least any egregious errors have gone unreported).
Thus the timing of the Tax Foundation updates works well: by ~mid-February of any year, people seeking "accuracy for federal and state filing purposes" should be using commercial tax software to prepare the previous year's taxes, and using the previous year's state tables for the first ~1.5 months of the new year is probably well within the margin of error for predicting brokerage income, etc.
Perhaps a longer reply than needed, but your question gave me the impetus to think through what I had only vaguely considered.... Further feedback welcome!