I have a box edition of Witcher 3 GOTY edition that i bought a year ago and played some of it. Now i wanted to get back to it. Since i have new hdd and new system, i just installed the game from discs, but after that, gog galaxy wanted to downlaod over 30GB of updates.
I tried to copy the game files from my old disk ( ~39GB) but galaxy still want to download additional 30GB of data after chechikng the files.
Was there really 30GB of updates in last year and the game takes almost 70GB right now?? Or am i doing something wrong?

Galaxy want's to update the game to the latest version. Yes, the client likes to download everything.

So there is no other way to actually play full game without 30GB download, even if i have box version on discs and old full instalation from year ago?...

That's... unfortunate. Main reasonn that i buy box games is that i dont want to downlaod huge contents apart from occasional updates, with my limited data internet connection :(

Had the same problem just trying to install the 20MB overlay.

This is was solved the issue for me:

Thanks!
I think it worked

Not everyone use galaxy

Hello =)

Why do the folders "bin + content + dlc" in the GOG GOTY v1.31 version weigh 14GB less than the set of Steam GOTY v1.31? Why does no one know the answer?
Who has the full version of GOG v1.30, how much does it weigh, with which languages are voiceovers?

Everyone refers to nonsense, like "in Steam music, artbook and stuff are downloaded". Are you blind? I indicated 3 specific folders with game files only. Why are they with one English voice acting so much less than in the version of Steam, with English + Russian voice acting? Localization does not weigh so much.

I asked for GOG support, they referred to Goodies ... hah. I asked support of the CDPR through the contact page, they did not answer me. I ask in the forums - silence ...

The issue is resolved.
On Steam there are directories \content\patch0 and patch1 with the weight of 1.09GB and 1.96GB, which are absent in the GOG GOTY. Also in the folder \content\content4\ there is a file streaming.cache weighing 6.06GB, which is also not in the GOG GOTY.
Thus, the Steam GOTY is 9.7GB more size.