On Feb 18, 2019, at 12:31 PM, KP <khaiphan9x@gmail.com> wrote:
I will mention some of the following stages:
- GMT+0: July 1, 1906 to April 30, 1911 (Indochina)
- GMT+7: May 1, 1911 (Indochina)
- GMT+8: 23:00 December 31, 1942 (Indochina)
- GMT+9: 23:00 on March 14, 1945 (Empire of Vietnam)
- GMT+7: September 2, 1945 (Democratic Republic of Vietnam) and July 1, 1955 (État du Viêt-Nam)
- GMT+8: 23:00 on January 1, 1960 (Republic of Vietnam) and GMT+7: January 1968 (Democratic Republic of Vietnam)
All of those are outside the scope of the tzdb.
- GMT+7: June 13, 1975 (Republic of South Vietnam)
Thus, Vietnam time has been different in 1945 (Saigon/HCMC does not exist) no longer in Indochina time. As mentioned, a small change can also lead to a timezone. It is possible to create a time zone for Hanoi from here according to the historical facts I mentioned.
There *is*, in backzone, a tzdb region "Asia/Hanoi". It converts all times starting with 1970-01-01 00:00:00 UTC to local time in the same fashion as Asia/Bangkok. It converts times *prior* to 1970-01-01 00:00:00 UTC differently from Asia/Bangkok.