KP wrote:
- After merging with Ha Tay, Hanoi (capital) is the largest province in Vietnam
tzdb goes by cities, not provinces. citypopulation.de estimates a population for Hanoi (including Ha Tay) that is less than that of Ho Chi Minh City. https://www.citypopulation.de/Vietnam-Cities.html gives 2017 estimates of 7.4 million for the former, and 8.4 million for the latter. Although both are growing, the ratio of Ho Chi Minh City vs Hanoi (including Ha Tay) population also appears to be growing, suggesting that Hanoi is not catching up. Even if Hanoi became somewhat larger than Ho Chi Minh City, the following guideline in <https://data.iana.org/time-zones/theory.html> would still apply: "Do not change established names if they only marginally violate the above guidelines. For example, do not change the existing name Europe/Rome to Europe/Milan merely because Milan's population has grown to be somewhat greater than Rome's."
- +7:00 (North Vietnam and All Vietnam since 1975) timezone has been the longest unified timezone ever
I'm not sure what's meant by "longest unified timezone ever". In tzdb, the location that has been at its current UT offset for the longest time is Atlantic/South_Georgia, unchanged since 1890. In contrast, tzdb's sources indicate that Hanoi changed UTC offset in 1954, which makes Hanoi less stable, time-wise, than Bangkok (last change 1920) or Lagos (last change 1919). At any rate, longevity of this sort has not been part of the criteria we've used to choose Zone names.