On Mon, 18 Feb 2019 at 15:32, KP <khaiphan9x@gmail.com> wrote:

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.

As has been pointed out before, we don't make new zones just because there are differences prior to 1970. Please read ftp://ftp.iana.org/tz/tzdb-2018i/theory.html and ensure you understand it. Ask if there is anything there you do not understand.

On Mon, 18 Feb 2019 at 15:32, KP <khaiphan9x@gmail.com> wrote:

It is possible to create a time zone for Hanoi from here according to the historical facts I mentioned.

And that has already been done in the 'backzone' file, which can already be installed by those who require that level of detail. See ftp://ftp.iana.org/tz/tzdb-2018i/backzone:

# Vietnam

# From Paul Eggert (2014-10-13):

# See Asia/Ho_Chi_Minh for the source for this data.

# Trần's book says the 1954-55 transition to 07:00 in Hanoi was in

# October 1954, with exact date and time unspecified.

Zone Asia/Hanoi 7:03:24 - LMT 1906 Jul 1

7:06:30 - PLMT 1911 May 1

7:00 - +07 1942 Dec 31 23:00

8:00 - +08 1945 Mar 14 23:00

9:00 - +09 1945 Sep 2

7:00 - +07 1947 Apr 1

8:00 - +08 1954 Oct

7:00 - +07

The ONLY question that remains open here is whether Asia/Hanoi should be moved into the mainstream distribution. As you will have seen from this discussion, there are several reasons for and against such a proposal, and those will require thoughtful discussion. Further arguments will not strengthen your case beyond that.

--
Tim Parenti