And imo that is not even an unimportant update. The impossibility to mix audio and subtitles to your liking was one thing I crizised in the release thread and look what they did:

"Options to play German, French and Russian subtitles with English audio
Microscope Puzzle difficulty more reasonable
Sync English audio of doll-craving intro scene (original game bug)"

Just went to check Finnish Business Information System-database and it says that Mindfield Games is bankrupt (as of 09/19/2017).
Database search-site -> https://tietopalvelu.ytj.fi/yrityshaku.aspx?kielikoodi=3 (search with Business ID 2578566-8)

Just got an reply from them on Steam:

"We are working on it. GOG have some technical issues with our games."

Makes me wonder what kind of technical issues those would be ...

Uru: Complete Chronicles may be out of date on GOG: https://www.gog.com/forum/myst_series/uru_is_out_of_date_on_gog

Because I don't own the game on GOG I don't unfortunately know a reliable way to access the game changelog.

Like the OP says, the most recent changelog is hotfix3.

Removed Lion's Song, the Soundtrack is now available.
https://www.gog.com/game/the_lions_song_soundtrack

Removed Katana Zero, The Mac version is now available.

Lumo won't be getting updated, note added.

Publisher: "The update on Steam was to fix a leaderboard issue, and there was an update to fix some controller problems.
But due to technical matters, there won’t be any more updates. Not to Steam and neither to GoG."

why is crypt of the necro dancer on there?
is the DLC not on gog?

Soundtrack DLCs missing yes. Some are here, some are not.

i mean u could put forager on the list but the developers are working to get gog achivments, the mac and the linux version on gog. There are just a few hiccups now, but i am in touch with the devs and they are working on it.

Added
The 7th Guest: 25th Anniversary Edition
Simulacra

Figment developers are working on getting the soundtrack on GOG, source added.

Added
Forager
Gone Home
Grim Fandango
Halcyon 6: Lightspeed Edition
Party Hard 2
Rise of Industry
Space Rangers: Quest (If anyone could direct us to a changelog for this one, or provide screenshots with version numbers, it would be appreciated.)
URU: Complete Chronicles

Updated Broken Sword 1/2 with a source for where to (legally ;)) aquire missing language files.
Updated King Arthur's Gold which is now F2P on Steam, has been removed from GOG since then, and never received the two paid DLCs available on Steam.

Got this info from official 'SNK-games' wiki.
Looks like link is russian only, sorry about that.

edit.
GOG forum still mess with the links...

Soooo... See attach below.

Thank you, the numbers are enough. :)

Updated Rise of Industry: Unable to download Steam Workshop items without Steam (via Steam Workshop DLer, for example).