On Wed, 27 Aug 2025 at 23:57, Munkh-Erdene Erdenebat via tz <tz@iana.org> wrote:

The Hovd timezone is observed in three provinces: Hovd, Bayan-Ulgii, and Uvs.
However, when I checked the tzdata files (zone.tab and zone1970.tab), it lists five provinces under the Hovd timezone. My understanding is that it should be only the three provinces mentioned above.

It appears you may be looking at an older version of tzdata files. In the latest release, 2025b, the two Mongolia (MN) lines in zone1970.tab read as follows:

MN +4755+10653 Asia/Ulaanbaatar most of Mongolia
MN +4801+09139 Asia/Hovd Bayan-Ölgii, Hovd, Uvs

As recently as July 2024, we made some changes to better reflect the information that had been made available to us about historical timekeeping in Mongolia:

https://github.com/eggert/tz/commit/7eb5bf887927e35079e5cc12e2252819a7c47bb0

This change, first released in version 2024b on 4 September 2024, removed Govi-Altai and Zavkhan provinces from the comments field for Asia/Hovd, bringing the formerly listed five provinces down to three.

If you have better data for the history of Mongolian timekeeping, backed by appropriate publicly-available news or government sources, we'd be very happy to hear about it as many of our existing sources are conflicting.

--
Tim Parenti