A few weeks a go I downloaded Etherlords and installed. Ran just fine, Etherlords II is better.
A few days ago I downloaded Submarine Titans and Throne of Darkness. Both games opened Galaxy after first time launching and inserted themselves into the Galaxy list of games. Etherlords did not do that.
After looking at the installers, I saw that all the newer ones had a number code in brackets in their names.
Did they stealth combine the Galaxy client with the offline installers again? It's kinda annoying.

I hope not. To be clear, you are using the browser, and clicking "offline backup installers", then clicking the installers from inside that menu?

I did through Galaxy and to be sure through browser. Both give me the same installer file.

Once installation is complete you get the button "Launch". if you press that, Galaxy will open and the game get's inserted in your Galaxy game list. If you close Galaxy again, it won't open itself again on further game launches. It's the first that's so annoying.

That's because of the installer is opening Galaxy (only if installed of course) and register the game in it. That means, Galaxy Service is already running before you click the "Launch" button. If you don't have Galaxy installed, the game will launch directly with that "Launch" button.

So don't press that launch button! :-P

Galaxy is installed but not running. And the main point was that the older installers are not doing that, so there must have been a shift in functionality at some point.

Technically, yes. Installers and patches.

Otherwise, no.

That means they haven't added the API that allows for Galaxy to detect installation to some older games (yet). But still, each game has only one offline installer.
For me, it doesn't matter, all single player games on GOG work fine without the need for Galaxy.

Some Galaxy Services are launching during the install process but not the GUI. You can check this while running your Task Manager if you install a game.

The older installers don't do that and if you want those games to be recognized in Galaxy, you have to add them manually. So yes, they changed that at some point in the past.

Did you already have Galaxy installed?

Not sure if you meant that the game installer installed also the Galaxy client, or that Galaxy recognized your installed GOG game, and launching the game starts also the Galaxy client, if it is installed.

I thought the latter has been there for ages, but then I can't be sure since I don't have Galaxy installed.

EDIT: Ok ok I guess this was clarified already.

That's not actually true.

Case in point: Divinity: Original Sin 1. A couple of years ago, they released on update patch for that game which included an unintended bug that removes essential, highly necessary tooltip information from the skills in the game.

As a result of this bug, the player is unable to see what level the skill they are looking at actually is.

This makes the game unplayable while it is like this. And non-Galaxy users have nothing they can possibly do to fix it, since GOG doesn't offer earlier & unbugged versions of the game for download. Hence, the broken & bugged version is the non-Galaxy user's only choice.

In contrast, Galaxy users can rollback to an earlier version before it become bugged & broken in the way I've described, and thus enjoy the game as it was intended to be.

The bug is solved now right? Are there others? I haven't seen a list of offline installers with Galaxy related bugs anywhere.

I haven't checked recently, since I used to try the "latest update" every 6 months or so to check if the bug was fixed, and it wasn't. So every time I updated, I always had to then rollback again, via Galaxy, to the non-bugged version. Eventually I stopped bothering to keep checking. But I wouldn't be surprised if it still wasn't fixed.

I'll check again when I'm able to do so in a couple of hours, and then edit this post with the news of whether or not that bug is still there.

And even if it isn't still there now, it certainly was there for an awfully long time.

As for lists of problems like this: I don't think anyone has made one. Even though the bug in DOS 1 which I've described was/is (depending if it's still there or not) game-breaking, it received very little attention, other than a few GOG customers (rightfully) complaining about it.

So who knows how many other games are bugged in their latest version, but the problems also receive little to no attention, so therefore hardly anyone knows about it. There could be many.

EDIT: I just checked the latest update to DOS 1, which is 2.0.119.430 KO. It still has the game-breaking bug in it, just like has been the case for the past couple of years now.