Stephen Colebourne wrote:
I'm simply asking the tzdb to provide reasonable local time information since the start of global offset fixing for the IDs it provides
That's being done for McMurdo -- as far as we know, its entry is accurate for all time stamps used since it was founded, and (as Russ Allbery pointed out) for time stamps before McMurdo was founded and for which localtime is undefined, it's reasonable to interpret the new entry as being more "accurate" than the old.
keeping the data stable if entries are guesswork.
That's not a reasonable request even for near-future time stamps that end users actually care about, much less for these long-ago time stamps for uninhabited locations, where they don't care. We're about to change near-future data (even though our changes are guesswork) for Tocantins and for Jordan. This is not because we *like* making guesses; it's because guessing is the best we can *do*, the system does not allow us to refuse to make these guesses, and better guesses are preferable to worse guesses.