As said above, same no changes happened for Steam version as well. Especially not happened for OP assumption. :| Dark Crusade and Soulstorm is not combinable even in theory. And not expansions. It is stand-alone expansion which entirely differ term although seems similar name. Usually it was used for old-engine new game while new-engine game in dev. Speaking of nowadays terms, they wasnt DLCs. While any else kind was DLCs (build-in AddOn or additional exe Expansion).
Stand-alone was rarely used for real expansions but not really stand-alone - just contain required base game. In our DLC/digital/subscriptions era that happened more often, cause now its not related to what is on the disc, but what is in subscription you bought.
Eg if you buy Counter-Strike and install in Steam you get Half-Life installed automatically. It is DLC sold as stand-alone.
Another example is Total War Shogun 2 expansions all of them are DLC AddOn's but one sold as stand-alone and actually you get regular Total War Shogun 2 in Library +one DLC and base content will be locked inside the game.
Third example is DoW Retribution DLCs, some of them sold as stand-alone. And Campaign sold as DLC. You always get the base game whatever you bought.
Speaking of Steam, there is no DLCs on Storefront there. Subs with DLCs packs. Not directly as DLC(s list) to the game.
Since GOG relate on setup exe files, it have actual DLC lists on store for each game and sold DLC as DLC not as subscription. It can have combined multiple DLCs in one exe as Extended Edition Upgrade DLC setup, but that mean one setup = one store item, always. For Steam actual list of DLCs you find only after buying in your Library for game Properties DLC tab.
Or in SteamDB before buying.
