Hello. Years ago I found somewhere a big thread of all Heroes 2 versions published, along with info about how music tracks are mixed up. I can't find it anymore, but here's what I learned:
Midi and CD versions are bit shuffled, so you may hear correct Midi track for the castle, while wrong CD track will be played if you switch. Just listen to warlock necro and barbarian tracks to learn that it just doesn't sound right.
I also learned that GOLD version is inferior to TSS + PoL , in a way that it mixes some tracks from both and flat out removes some, so you will never hear tracks that you would hear by buying the game in the nineties.
Downloaded sountrack is wrong. For example track marked as "expansion" can be clearly found in the H2 DEMO.

Now I don't want to start my investigation from the scratch if anyone actually figured this out before. Who knows, maybe someone can find that big thread that solved everything. My final goal is to post a guide telling how to swap files in order to have correct music for all the castles. Anyone willing to help?

Wasn't this fixed last year on GOG? They included the option to swap soundtracks between the original Succession Wars and expansion Price of Loyalty tracks with a handy command prompt. I have never heard the claim that either of these tracks are mixed up or omitted compared to the CD original.

Interesting. Wasnt playing it recently. But it turns out "16 bit stero no opera" plays no castle track. It uses grass/dirt etc track instead. Will investigate it further and publish my findings