neumi5694: Most of the games don't have ambient music anyway (I don't consider blowing wind being music) and the games which do, more often than not include that music in the OST, the master of all being Kingdom Come Deliverance with 200 ambient music tracks. I think in total it's something over 6 hours just ambient music.
idbeholdME: I also don't consider ambient sounds music. But in the TQ case, entire tracks were missing. All the generic music loops in all acts (about 3 for each act, each several minutes long), mini-boss combat tracks, shorter location tracks etc. A substantial part of the music from the game was simply not present in the soundtrack. I personally would expect something called "Official soundtrack" to be extensive and trying to contain everything. Especially when it's being offered for sale separately. I would never buy a soundtrack of a game I own in the first place, but even if I did not own the game, I still would not when I can't expect the soundtrack to be complete. TQ was the first game where I really noticed this discrepancy and since then, I am really doubtful of any "official" soundtracks.
Another example would be Enclave. Official soundtrack - 64 minutes, music straight from game files - 95 minutes.
Don't get me wrong, I am the first to believe and confirm that there are soundtrack with missing tracks.
I just don't think it's the majority.
If you're looking for another complete one, check the Turrican anthology on Bandcamp or Amazon.
Enclave ... I actually think they said it was just samples, but I am not sure. But yes, I found a much more complete version of it, but it's not labelet 'gog' in my directory :)
btw, your mentions of the Unreal games would be a good topic for a new thread: Games that
don't come with an official soundtrack (well, basically it doesn't matter), but where the music fils can be extracted from the game directory or an archive file (without requiering the decrpytion key for a Unreal Engine decompiler)
I also extracted the Monkey Island SE soundtracks, but they are not listed as 'gog' soundtracks. Jedi Knight and X-Wing use the classic Star Wars soundtrack without changes, so that could be mentioned as well.