I also wonder about the 0,2%
(a) It's test accounts by some guys from gog?
(b) Is there any way to cheat Achievments in gog Galaxy like SAM for Steam?
(c) is it working now? Has anyone had success?
That 0.2% are people that asked the GOG support to unlock those achievements by hand.
This is not the first game with broken achievements (likely due to poor implementations by game devs), like in Styx: Master of Shadows. In that game, there are some broken achievements too, with a percentage of 0.1%. Yeah, that 0.1% it's me \^_^/ (and a handful of other guys/girls)