I don't know if you can answer this, but as I'm in Germany, the adult patch is unavailable to me on Steam. I assume the itch.io adult patch is incompatible with the Steam version? Do I have to get the game/DLC a second time to access the adult patch, this time via itch.io? (I honestly wouldn't mind it that much because I truly love adwd, but money is always tight.)
Edit: I could have just tried it before writing this comment, as I dropped the file from itch.io into my game folder from Steam and it shows up as installed. I'll test it out another time.