I've tried it both ways, without success, unfortunately.

I bought The Vanishing of Ethan Carter on Oct 29, 2016 and the key for The Vanishing of Ethan Carter Redux worked fine.
(Well, I always download installers and check the serial key, so I redeemed it the same day I bought the base game.)
If your key is invalid, you should contact GOG Support.

Some other GOG games also have this kind of keys:
Baldur's Gate: Enhanced Edition
Baldur's Gate II: Enhanced Edition
Divinity: Original Sin - Enhanced Edition
Icewind Dale: Enhanced Edition

Note that Planescape: Torment: Enhanced Edition do not provide a key for Planescape: Torment.
It just add Planescape: Torment to your Library if you does not have it yet.

Some games also provide extra/bonus key so you can play the multiplayer game with friends:
https://www.gog.com/forum/general/bonus_games_included_in_gog_games/post10

But it is a serial key. Here is what I could find in my account
The Vanishing of Ethan Carter Redux http://www.gog.com/redeem/4XE2C4AB

The 4XE2C4AB is a normal GOG serial key which I could have given away if I wanted. However that is not the case with i.e. the SVGA version of LSL which is a bad example since this basically is a game pack consisting of the games 1-6. You have a point with the Star Wars example though but again - I prefer it this way because you can gift the keys if you don't want them.

I agree to your point but I just mentioned BG to show that you always needed to use this special menu point when you had additional serial keys included to your game. So this is not that hidden.

Well - they explained when the version was released and they still have the information about this additional version on their gamepage.

https://www.gog.com/forum/vanishing_of_ethan_carter_the/redux_edition_out_now/post33

I am sure that this is a mistake GOG made and I am quite sure support will help you here. Like said it's still listed on the gamecard therefore still part of the package. So of you have not gifted away the key it must have been a mistake. To answer your second question: yes, it will be added as an additional seperate game in your library.

Thank you for yet another useful link I just had to bookmark :)

This reminded me that last summer I got Wasteland 2 in a piñata, so I went to my library to check whether it came with a Bard's Tale (2004) key, which in turn comes with the original trilogy. And indeed both my Wasteland 2 library entries (regular, and Director's Cut) have a "Serial Key" tab, but they're empty. :P

I hope you contacted support about it?

I haven't, since I assumed it was not like a 'regular version' of Wasteland 2 (i.e. it has, or at least it originally had, a different library game ID than the game ID sold in the store).

But now that you mention it, I guess it's worth asking about.

A lot, actually:

Wasteland 2

Game goodies:
· manual (4 MB)
· reference card (1 MB)
· map (90 MB)
· soundtrack (4 choir songs, FLAC) (27 MB)
· soundtrack (4 choir songs, MP3) (10 MB)

Digital Classic Edition Upgrade goodies:
· Wallpapers (1440p) (3) (8 MB)
· Official Soundtrack (MP3) (102 MB)
· Official Soundtrack (FLAC) (590 MB)
· soundtrack (4 choir tracks, FLAC) (27 MB)
· soundtrack (4 choir tracks, MP3)) (10 MB)
· Concept Art Book (4 MB)


Wasteland 2 Director's Cut

Game goodie:
· Director's Cut manual (16 MB)

Wasteland 2 Digital Classic Edition Upgrade goodies:
(Same as for Wasteland 2)



But it doesn't include a key for The Bard's Tale (2004).

Asking is never wrong. I ask so much that people are trying all kinds of things to make me stop ;)
No, seriously. Support is nice and at least they will tell you something in best case they will fix this.

Edit: But since Grargar already supported you there probably isn't much to fix at all :)

You have the Classic Edition. It should come with a code for Wasteland 1.
Bard's Tale (2004) is only available with the Deluxe Edition.

Oooh, I see. The Bard's Tale (2004) key comes with the Digital Deluxe Edition of the game, so I should buy the Deluxe Edition Upgrade, which I don't own, in order to qualify for it.

Never mind, then. :P


EDIT: Ninja'd.

As a matter of fact, I didn't get a Wasteland 1 code either. But I don't really care since I already owned it.

Just got an update flag for The Witcher: Enhanced Edition. Is this a delayed flag or something new?

I was just about to install that. Good timing.

Oh wait, it's a Galaxy update. Okay, fuck that. :P

Italian and Polish manuals and game guides have been added:


---------------------------

Games included in this batch:

· This War of Mine: Stories [Season Pass] [DLC]
· Witcher: Enhanced Edition, The

---------------------------

A game has been added: This War of Mine: Stories [Season Pass] [DLC]

---------------------------

Witcher: Enhanced Edition, The has changed

>>> Bonuses changed *FROM* manual, manual (German), manual (Russian), 18 wallpapers, game guide, 2 maps, game guide (German), music inspired by The Witcher (MP3), soundtrack (MP3), music inspired by The Witcher (FLAC), soundtrack (FLAC), 7 behind the scenes, 5 creator interviews (Atari), 9 creator interviews (CD Projekt RED), music video, 26 avatars, artbook, The Witcher calendar, The Witcher story *TO* manual, manual (German), manual (Russian), manual (Italian), manual (Polish), 18 wallpapers, game guide, 2 maps, game guide (German), game guide (Italian), game guide (Polish), music inspired by The Witcher (MP3), soundtrack (MP3), music inspired by The Witcher (FLAC), soundtrack (FLAC), 7 behind the scenes, 5 creator interviews (Atari), 9 creator interviews (CD Projekt RED), music video, 26 avatars, artbook, The Witcher calendar, The Witcher story


[FILE UPDATES]

* File added: game guide (Italian) --- Name: the_witcher_enhanced_edition_game_guide_it.zip --- Size: 5.2 MB --- Date: Wed 15 Nov 2017 13:28:52 GMT --- Version: [empty]

* File added: game guide (Polish) --- Name: the_witcher_enhanced_edition_game_guide_pl.zip --- Size: 1.5 MB --- Date: Wed 15 Nov 2017 13:28:51 GMT --- Version: [empty]

* File added: manual (Italian) --- Name: the_witcher_enhanced_edition_manual_it.zip --- Size: 1.3 MB --- Date: Wed 15 Nov 2017 13:02:44 GMT --- Version: [empty]

* File added: manual (Polish) --- Name: the_witcher_enahnced_edition_manual_pl.zip --- Size: 1.4 MB --- Date: Wed 15 Nov 2017 13:25:05 GMT --- Version: [empty]


[NO CHANGELOG]

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Forget about that. They no longer have 'In development' as a Feature.