Completely agree with Marko, I'd add that after all this time GOG should have started actively interacting with threads like this one or open a direct official channel with proven users if they really don't have the time to unearth missing updates themselves, but nothing has ever been done about it. Having to open tickets every time that serve absolutely no purpose is just a waste of time.

Probably a huge waste of time, but I am contacting devs/publishers about delinquent updates once again. These are the few that I have reached out to already:

Nicalis - The Binding of Isaac 1.7.9
Mossmouth - Spelunky 1.47
The Digital Lounge - Another World 20th Anniversary "2020 update"

Not going to hold my breath on hearing anything back from these entities. Likewise with having these suddenly popup here fully updated, but stranger things have happened. I very much urge others to ramp up their contact with any devs/publishers about their missing updates and hopefully it will help bridge the gap that is getting further out of control.

That reminds me, I think it's been 3 months since I opened my first ticket for Isaac (only got a reply for the second in august) and I am to believe they actually forwarded anything? yeah bs
And I expect even less from Nicalis, the first post-GOG release update took ages to arrive too.

What can GOG do if the developer does not want to bring the patch/DLC or thinks the patch is not ready for GOG?

Bride them? Send a monthly email asking if the patch is ready. How many resources would it take GOG to focus on ensuring games get updated??

Urbek City Builder seems set on not bringing the DLC/update to GOG. If that's the case, we or GOG can only do a little.

What MarkoH01 said seems to be the only thing we can do.

Yep. I informed GOG about the Mac version of Ozymandias being outdated, they basically said "thanks we'll look into it" and did nothing. So after waiting too long, I contacted the dev, and within an hour of responding, the Mac version was updated on GOG, complete with the offline installer. (So I really don't want to hear any devs complain that GOG updates are "too hard" and I also don't want to hear that the offline installers need any manual work on GOG's side.)

Enforce that requirement that I understand actually exists in their distribution contracts, of receiving the update within two weeks, by actually applying penalties if it doesn't happen?

Penalties the developers?
This makes me wonder why some devs act like updating the GOG version is so hard. We have a single man Dev updating the GOG version weekly.

Publishers, probably, since those are the ones they have the contract with (of course, for actual indies, it's the same thing). And yes, withhold payments until the situation is resolved and going all the way to delisting if months and months pass or the situation keeps repeating.
("But this will scare away devs and we'll get less games!!!" Yes, scare away bad devs/pubs and bring less unsupported games. Good.)

Scaring away devs is the only downside I see. GOG can play tough or continue letting the devs/Publishers walk over them.

Destroy All Humans! 2: Reprobed is missing the "Summer Patch!" from June 21, 2023, which is known to fix performance as well as other misc issues. Last update on GOG was in April 2023.

I'm glad I never picked this game up.

100% agreed!

Perhaps GOGDB's front page should have two new sections for the top then worst publishers and developers based on how badly their games maintain update parity between GOG and Steam, as while the average gamer tends to only care about the Steam releases being kept up to date, that would still leave us a lot of Steam only customers who might find it very distasteful to continue buying games from such publishers and developers once it would be easy enough for them to check out who the worst offenders are.

Looks like GORD got it's update now. Can take that off the list.

Suggest them to leave the store if they are not willing to update the GOG version (anymore). I think there are quite many games that have left GOG for such reasons, not sure in how many cases GOG has initiated the thought-process of leaving GOG (if unable/unwilling to update the GOG version).

A separate case is those instances where the developer has meant to update the GOG version, but it hasn't been updated for some reason, like they just sent the update to GOG HQ in Warsaw and expected GOG to perform the update, or something. We have had those stories, true or not, as well where the developer has said they have "sent"(?) the update already to GOG, but the game is still non-patched.