I've installed a few games recently from offline installers. Galaxy recognizes the base as installed, but not the DLC. This hasn't always been the case, though it's been inconsistent. Tyranny, for example, a year or so ago when I upgraded to the Deluxe Edition and installed the DLC from the offline installers, it recognized some, but not others.

The latest game I installed was Prey. I downloaded the offline installers for the game and DLC. I installed them, and Galaxy recognizes the base game is installed, but not the DLC. It's definitely installed because I can start it stand-alone or in Galaxy and access the Mooncrash DLC.

What's weird is that if I right click it, it shows Additional executables > Prey: Mooncrash, but if I click Manage installation > configure, it does not show Mooncrash as installed. I tried verifying the game, and it downloaded 28MB, but still shows it not installed. I checked the box for the DLC from the configure window and it began re-downloading the 16GB DLC instead of checking to see if it was already there.

Yeah Galaxy 2.0 is broken when it comes to detecting DLC installed with the offline installers. I put in a bug report for this a few weeks ago.

I have a fix, it's a bit convoluted but it works in all cases I've tested.

1. Rename the game's installation folder to something else Ex. C:\GOG Games\PreyTemp
2. Uninstall the game from within Galaxy. Since the folder has been renamed, this will do nothing except generate an error message, but it changes the game's status in Galaxy to uninstalled, which is what we want.
3. Rename the game's installation folder back to the original name. Ex. C:\GOG Games\Prey
4. On the game page in Galaxy use "Manage Installation -> Import Folder" to re-add the game to Galaxy. This will re-add the game AND properly detect all the installed DLC.

Hope that helps for now.

Thanks. I remember having to do that with the old Galaxy a long time ago. You can skip the uninstall part if you move/rename the game's directory while Galaxy is not running. When you start Galaxy it will remove it from the installed list. Then move/rename it back, right click the game, import, select the folder and it puts it back.

I just did it with the games missing DLC and it does now see them installed.

Ah nice, that'll save a bit of time when I need to do it again.