Just to clarify. Only very few yechidei segula fasted two days, Some very special people. One of them was Rabbi Levy Krupenia, later Rosh Yeshivas Kamenitz in NY.
Another point I would like to clarify is who’s psak held the earlier Yom Kippur.
Thirdly, regarding Alaska and Hawaii, I think more Hawaii than Alaska. It falls between the International Dateline and the Halachic dateline according to one opinion.
Lastly, I heard a shiur from an expert in these matters, Rabbi Jeremy Stanton in Manchester. He pointed out that in all resident communities of places that fall in doubt, they keep Shabbos on the day that is Saturday in that place. So that is New Zealand, Japan, Hawaii etc. And the shaaloh is only for visitors who wish to fulfil the correct halacha. They must nevertheless not do melocho in public on the day that the locals keep as Shabbos.
What would be interesting is Samoa and Tokelau that changed to the other side of the IDL in 2011. The day after Friday 29 December 2011 became Sunday 31 December 2011. I believe Shabbos would be correctly observed there on a Sunday.