Geralt_of_Rivia: This is a complete list of current duplicate slugs on GOG
mrkgnao: I don't think one can have a "pack" in one's library, only a "game", so I'm not sure any of the game-pack pairs are an issue here. And I don't think the DLCs are an issue, either. This only leaves the bizarre pair of Thronebreaker games, unless I missed something, but I don't know how one can get two different copies of the same game in one's library.
To be honest, I still don't properly understand the problem, but l guess that's just me.
Yes, seems to be the case.
The Sam & Max games do definitely have different slugs now, though they may not have when the report was made.
I do own Thonebreaker but only the version currently for sale, so that's not super helpful
Edit -
The problem was that the duplicate slug resulted in gogrepo trying to store the files in the same folder, and then verification not working ( because it would find alien files for whichever it was trying to verify ) or worse if there were duplicate file names in which case you could have exciting collisions during download.
I don't see anyway to verify this at the moment though, since the issue seems to no longer exist on the GOG side unless someone owns both Thronebreakers.