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Will the patchnotes be available?
This question / problem has been solved by FlockeSchneeimage
Patchnotes were added to the Changelog-Tab. (If you haven't already noticed.)
But according to the changelog thread, it seems Gog is a bit behind Steam.
Here it's 1.5.10, and on Steam it's 1.5.11.

Why is it not up to date?

I'd rather buy it on Gog since it's currently cheaper, but since the Wolcen thing (it's been taken off before full release), I tend to buy only full released games on Gog.