Hello!
So what most likely happened is I was going through my Steam library in efforts to keep it from getting bloated, getting rid of the games I don't need, as in the ones I don't play anymore/lost interest in/didn't enjoy and don't plan on giving them a "second chance", ones that don't work anymore (like for example MINIMAL from that sgtools list, actually), or straight up "meme games" that are often gifted as a joke and are, at best, garbage, and so the games sgtools shows you most likely got hit during that proccess, and considering there was a period of time when I wasn't active on this website (from 2016 or so until recently, you can see it in my stats), and all those games are from before that period of inactivity (2013-2015 I believe) (and in some cases of questionable quality but my subjective judgement isn't of any importance here), I'm inclined to believe I didn't consider the way I obtained them while going through my library, though I do remember playing them or at least giving them a go a long time ago after checking them.
Not all of the games I won were "lost" this way, but I agree a 5 out of 16 isn't a perfect score by any means and you are justified in being concerned.
Considering your giveaway, I can tell you that I have bought, played and enjoyed SOMA and Amnesia: The Dark Descent by the same developers, and do intend on redeeming Amnesia: Rebirth and playing it, as I have done with the rest of my "wins" (except for Clear Sky but I've played it a lot before I owned it on Steam so I'm fine for now), my Steam profile is open so you can look for them if you'd like to double-check.