In November 2017 I download Elminage Gothic, file setup_elminage_gothic_2.0.0.1.exe, filesize 510,609 kB.
Today I checked my account for updates and found the file setup_elminage_gothic_1.0_(20749).exe, filesize 514,525 kB.
Which one is more recent? I didn't see any mentioning of a patch between 2017 and 2019. Has GOG changed the version numbering system? I must say I'm confused.

The second is more recent, but you don't need it. Believed to be possible installer-only update?
They did change the version scheme. Old scheme was the GOG installer version. New one includes the actual game version in the the filename. E.G. it's better.

Thanks. I guessed that this might be the case, as the size of the exe file hadn't changed. And I prefer the new version numbering system, too.