I tried to put that link too but it won't let me post links for some reason so I couldn't, lol. Mine says "Connect now" in GOG Galaxy too but when I click connect it wants me to put in a code, but I have no code to put in. The game was gifted to me and I already used the gift code on the website. So, not sure about that one, lol.
MidnightAngel: I figured out how to. It won't work in GOG Galaxy (At least not for me & a lot of others), but you can get it from the website. You just need to go into your library, click on it, download ALL 3 of the files. After they're all downloaded, open the .EXE file (other 2 are bins), and click install. It should download just Book 3 for you if you have the others installed.
I hope it works for you! :)
JannyBee: Ah so the 5.55 GB file (or the 3 files that add up to that; I'm using the old GOG Downloader, which, by the way, seems to still work fine, so far that is) is INDEED Book 3? Okay, that's good to know, I was confused cause I never got an updated-notification and the files are labeled ver 2.6 when you download them manually.
Ya, it seems so. It worked fine for me. I downloaded all 3, then installed and launched it. Book 3 was there :)