Here's an interesting bit of info for anyone who owns A Hat in Time on GOG: When the devs finally released the most current updates on GOG a couple of months ago, they labelled the new version "GOG final" - and we all speculated that this might mean they don't intend to patch the game here ever again. But the game just got a new update today, in time with an update on Steam (which has no patchlog). So maybe they will keep updating the game on GOG after all?

Final in the context of software development simply means the application is ready for release.

Just seeing that list of problems makes it clear GOG needs some quality control. Either the developers simply don't care, or there are some communication problems on GOG's side (which wouldn't surprise me in the least).

If a game releases on GOG and it's missing features and missing VERSIONS outright (why you hatin' on Linux, guys?), then...what's the point?. It only chases people away from ever buying games on this platform.

True, but none of the previous versions released on GOG are labeled "final", so the assumption was that there's a reason why they went from using version numbers to calling the most recent one "final".

Disaster Report 4: Summer Memories is missing the free costume pack that is supposed to be inside the game acording to the GOG Gamecard but this is not the case (which btw makes this false advertizing). Will create a support ticket when I find the time (it takes time to kill the support bot ;)) but for now this is missing on GOG even though Steam actually has it.

I might be a little early on the draw, but Besiege just released a major update that has yet to land on GOG.

I'm hopeful it will show up here soon, but ever since Besiege added support for the Steam workshop, support for the GOG version has dwindled.

This link works, at least for me:
https://www.gog.com/en/game/succubus_demons_of_the_past

According to this post by ciemnogrodzianin who monitors prices on GOG, not only do we not receive updates for THE KING OF FIGHTERS '98 ULTIMATE MATCH FINAL EDITION and THE KING OF FIGHTERS 2002 UNLIMITED MATCH, but we also suffer price increases for the phantom updates.

This post from user idbeholdME reports a problem with King's Bounty: Dark Side.

The Ditzy Demons Are in Love With Me - Missing DLCs
- 18+ Adult Only Content
- Fandisc
- Fandisc 18+ Adult Only Content
- Fandisc Theme Songs

Ne no Kami: The Two Princess Knights of Kyoto - Missing DLCs
- 18+ Adult Only Content
- Art Book

Ne no Kami - The Two Princess Knights of Kyoto Part 2 - Missing DLCs
- 18+ Adult Only Content

About missing adult contents, I think it's worth noting those games were released before GOG allowed uncensored contents in their store.
Still, I'm going to drop a message in their Discord group asking if it'd be possible to add the missing contents.

Update about Sekai Project:

First, most of their games pre-GOG's change of policies regarding porn are missing contents.

Second, I asked about releasing the missing contents for all of their games, and a member of the staff replied "Takes time. Please be patient." Sounds like either something is already being worked on, or they're planning to do it already! =D

I was able to download the fix separately just now via requesting access to the Google Drive of the fix from its creator that's in the Steam link. I was approved quickly.