seppelfred: I pre-ordered Little Nightmares two weeks ago, it's in my library and I can download it without a problem.
But in the "popular"- list on the frontpage it isn't marked grey like all the other titles I own. And on the gamecard it doesn't say "owned". It seems like the only item I own is the soundtrack for the game. It was a pre-order bonus, but is now sold seperately. Very strange.
Welcome to the "GOG uses different IDs for the same title" game.
The reason the game doesn't show as owned is that the one in your library (i.e. the pre-order version) has a different ID than the one sold on the store now. Happens with most crowdfunded titles too - if you got a game as a backer, i.e. redeemed a code handed by the devs/pubs, the ID is more often than not different . That's also the reason that when you wishlist a game while it's in the "coming soon" or "pre-order" phase, it vanishes from your wishlist and you have to add it again when it's properly released.
What's worse though, is that more often than not, you don't get update notifications for such games.
GOG knows about these issues, but we have yet to see a fix.