Ok. I've done so.

Before I buy, I would like to know : are the audio tracks for HoMM 2 corrected ? Better encoding for CD tracks, glitches / looping problems removed ?

Thanks.

Replying to myself : the audio problem (probably due to bad ripping) at 0:30 on Warlock castle theme (homm2_05.ogg) is still here, 4 years after being reported. We can safely assume that GOG will never correct it.
I guess I'll have to chase a retail CD of Homm2 to get proper audio.

Same issue for Disciples 2 + Rise of the Elves OST in mp3 (in flac corrupted track is missing). Better to contact support with full ost file archive name, name of mp3 file (and\oe flac) that is corrupted. Sometimes it maybe be updated. When somone personally interested in this have time to correct the issue.

I read 3 posts before it has already been done :

https://www.gog.com/forum/heroes_of_might_and_magic_series/homm_25_soundtracks_minor_update/post17

But good news : in the extra/goodies, "Heroes of Might and Magic II OST - 06 - Town - Warlock.flac" seems to be *not* corrupted. So we can do sth like this :
ffmpeg -i "Heroes of Might and Magic II OST - 06 - Town - Warlock.flac" -vn -acodec libvorbis -q:a 10 homm2_05.ogg
Then put it in C:\GOG Games\HoMM 2 Gold\MUSIC\sw

That is good news, and very interesting. (I'm downloading the flac files now to to confirm.)

As you know, I reported the glitch a long time ago; and from memory, the response from GOG support essentially told me that they'd confirmed the glitch, but were unable to fix it.

I assumed it was because they didn't have access to a non-corrupted version (or that they were only licensed to sell the version they had, or something like that.) But if the version in the 'goodies' is uncorrupted , I see no reason why they can't now update the game files. Perhaps they just didn't have access to that file at the time.

(And yes, while typing this message I was able to download the flac files and I've confirmed that it does not have a glitch at the 30 second mark.)