On 2021-03-03 03:59, Tim Parenti via tz wrote:
A quick bisection puts the changeover, as far as The Air Almanac contemporaneously reckoned it, between November 1960 and March 1961.
Previously, our data had Tonga transitioning to UT+13 in 1941 based on a quotation from a 1997 news article. Although this differs from what the Almanac suggests by some 20 years, the article does mention a change coincident with the New Year, and that Tāufaʻāhau Tupou IV was Crown Prince at the time. As his predecessor and mother, Queen Sālote Tupou III, reigned from 1918-04-05 to 1965-12-16, a possible transition of 1961-01-01 still jives with the gist of the article, even if the specific year was perhaps wrong or just misprinted.
For what it's worth, our commentary already noted that Shanks & Pottenger had put the transition even later, at 1968-10-01. Although of course we don't know how they arrived at that date, given that they did, 1961 seems rather less out-of-place than it otherwise might.
While you are at it, let me quote [Ian R Bartky: "One Time Fits All: The Campaigns for Global Uniformity". Stanford University Press. 2007. p 24..26]: 3. On 10 September 1945 Tonga adopted a standard time 12 hours, 20 minutes in advance of Greenwich. On 19 October 1960 the legislation was amended by shifting to a time 13 hours in advance, and continuing the Eastern reckoning of the days. Tonga's daylight saving time, observed in 1999 and 2000, was abandoned by 2002. I thank Rhys Richards for these dates. This implies that tzdb is wrong for Tonga at least from 1945-09-10 until 1960-10-19, and it is compatible with your proposal for the switch to UT + 13:00 at 1961-01-01. And it suggests that the switch from LMT to UT + 12:20 should be advanced from 1901 to 1945-09-10. Michael Deckers.