So wouldn't that mean in the future when the game's servers are down, if you install this game using the installer that you backed up, this stuff won't be accessible?

The last time I started the game the content drop wasn't available, I'll do it later (without being connected to the internet, so that the game can't connect to their server) and report. Good question, btw!

Thanks for checking, it'll be interesting to read your results. Unfortunately i was connected online when i played it yesterday. I think i remember seeing the new content when i played either yesterday or maybe even the day before. So this content might have been added to the GOG version 2 or more days before the patch notes that were just posted on the GOG version today. Not sure when the last time you played while connected to the internet but you might already have the new cosmetics without realizing. I didn't get any sort of alert about it i was just looking around in my stash and saw them.

The content is there for me too. And you're right, they could have unlocked it a few days before. Someone should try to use an offline installer (which has not been updated) and start a new game fully offline, to be really sure. Or we could just get a technical answer from Techland. But I think that the newer installers (as soon as a new update comes) will contain everything previously released anyway.

Changelog for Update Content Drop #10 (added 30 May 2018):

- Content Drop #10 is here.
- Become a mysterious survivor known only as Badlands Rider. Chase down enemies in your signature buggy and bury them deep with a new machete, crossbow and shotgun.

Content drop 10 (and possibly others) is unavailable for offline installers with internet disabled at the time of posting this.

you can follow the discussion regarding the matter from here. few posts ahead and few behind

I was wondering why I had no latest contents, and now I know... and this SUCK... this is not right at all !

I don't want to install Galaxy for a game that I just play single player locally...

i've recently installed the game with internet connection but no galaxy. i'm not seeing the dlcs. activation no longer working?

Changelog for Update Content Drop #10 hotfix (added 28 November 2018):

* Minor installer bugfix.

Hmm, game is updating right now with 3 GB? Seems like an error in gog galaxy or is that really a new patch?

EDIT: NEVERMIND, see post below.

Update 1.17 (30 May 2019)

*Fixed an issue that caused the game to sometimes crash on Windows 10
*Minor bug fixes
*General build stability increased

Changelog for Update 1.18 (added 10 June 2019):

* Early game difficulty tweaks
* Late game difficulty tweaks
* Minor UI additions
* Added a new exotic mutation to an infected type

CHANGELOG Update 1.19 (27 August 2019)

New Features:

*Silver Hazmat - new opponent in the game, based on Gas Tank:
*HP +80%
*Exp 340
*Speed 1.1
*Increased drop rate for Gauze
*General fixes:
*Live events on/off - added functionality to turn off live events
*New option in Options -> Online -> Live events. Defaults to "on"
*Visible only during Live Events (change only possible while in main menu, during game grayed out)
*Turning Live Event "off" works for all (current & future) events

*When joining game to host with different setting, game will toggle setting accordingly to the host. Changed setting will remain after session ends (so if player have Live Events "off", joins someone with Live Events "on", his setting will remain "on" after session ends and will have to change it from main menu).