Thanks for making that information clear to me. This document is very useful for explaining why things are formed. 

On Mon, Jun 29, 2020 at 7:42 AM Paul Eggert <eggert@cs.ucla.edu> wrote:
On 6/28/20 4:17 PM, pierreneter wrote:
> if Asia/Bangkok represents areas with a time zone
> of +7, then why was Asia/Ho_Chi_Minh created?

Among other things Asia/Ho_Chi_Minh differs from Asia/Bangkok for timestamps
from 1959 to 1975, when south Vietnam was at +08 while the rest of the region
was at +07. tzdb identifies timezones where clocks have agreed since 1970, and
since these regions disagreed from 1970 to 1975 they need distinct identifiers.
For more, see <https://data.iana.org/time-zones/theory.html#naming>.