QWEEDDYZ: There is always two games (RotE completely separate differ game).
First Disciples 2: Dark Prophecy. Later two expansions, when you install all three of them in same folder + 2.01(than 2.02) pacth - they converted to extended game version
Disciples 2: Dark Prophecy - Gallean's Return.
Later it be released as separate editions (GR and Fantasy Pack in 2003, Gold in 2005, 2006).

GR is a base Disciples 2 game +addons included. Starting from 2005 Gold (4 CD NA edition) releases mistakenly put most maps to RotE Exports folder. If you copy them back - you get complete Disciples 2 game (GOG missing Impire.sg map). So addons included been mean - 4+4 campaigns, 2 for each faction, and every new maps from GotL and SotD.
Also 12 pre-exported leaders from devs are also missing in GOG (restored in very last build - but only for offline build). Download offline build and make GOG Galaxy find it if you still want to use GOG Galaxy client.

RotE is not a Disciples 2 game, technically. Completely separate. Although maps are compatible from 2.02 to 3.01. But even leaders are not compatible. You can copy-paste those 12 blank heroes, and they work. But stats scroll when you import them in scenario will show wrong stats (actually correct, but with minor bugs).

RotE in GOG is not a Gold version and even not fully patched! Find thread about "RotE is RotE Gold" and download from there RotE Gold Upgrade. That be enough for GOG RotE, but Impire.sg map from GR still be missing.
Copy-paste maps from GR to RotE as well as base game maps from RotE to GR (that be mistakenly placed only to RotE).
Here the full scenarios list (correct, except only 1 Tutorial listed)
http://nevendaar.com/index/0-43
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Just remind you
Rename ddraw.dll file (to _ddraw.dll)
Dont forget to start ConfigEditor.exe as admin. Properly configure game settings.
Set game exe "admin run" or use GOG Galaxy or Steam and set galaxy.exe\steam.exe "admin run".
Make sure game works at chosen settings.
Rename ddraw.dll back. Start DXCFG.exe as admin. Properly configure that. You can set your display native resolution, but keep Aspect Ratio enabled as set by default. Same as for video driver control panel.