Does anyone know how to make the patches work with the current Gog version?

The latest version that GOG.com posted up for this game is 1.2. Is there any possibility of GOG.com to introduce patches for different versions, notably patches 1.3a or 1.3b?

I've tried to download the actual dd_13.exe file from FilePlanet and it said it cannot find the game installation folder. I placed it within the Gog.com's actual folder for the game and it still doesn't detect the game, which is pretty weird.

The reason for the patch 1.3a is because I'm trying to play from an AAR by Ironhead_5 (US Army Major, or supposedly), which would teach me how to play as Germany and to understand the HOI2 basics.

Have you tried the patch here : Patch 1.3b ?

But I don't understand why you have v1.2 : I personally have v1.3a ? (I even remember my own old thread concerning my questions about 1.3b)
If you want to be sure about your version, you should go in the installation folder "C:\GOG Games\Hearts of Iron 2" and take a look at the "ReadMe.txt".

Hope this helps :P