I've recently started backing up my collection, so I thought I should get some clarity on this.

When downloading a backup installer, does it also include dlc and patches? Like, if I were to install a game that way, would it already be the most up-to-date version? Or would I need to download that stuff separately? Thanks in advance.

Most games won't contain all the extra DLC's, especially if they're bought separately later on. Also, I've downloaded patches along with offline backup installers before, and when I go to install the patch over top of the newly installed game, it tells me it's already up to date. So, I doubt you need to install the patches, but you can still do it for peace of mind.

EDIT: Any extra DLC's and patches that DON'T come with the main install file of the game will be in the list right below it.

I think nowaways GOG just updates the installers instead of providing patches. Which means that yes, on the one hand, downloading the installer should give you the most up-to-date version, but on the other hand, if a title gets updated again, you will have to download (and possibly re-install) the whole game again instead of just a small patch.

In any case, if there's a patch among the downloads, you just need to compare its version number with that of the main installer to see whether it's still required. They're listed next to the files.

DLC are always extra, if they are separate purchases and not integrated into the main game.

Base game owners only have installers for base game.
DLC owners will have installers for DLC, which is seperate with the base game installer.

Exception:
If you have GOTY or similar FULL version of a game, the installer will include everything ( non-GOTY base game and all DLCs).

All GOG games provide offline installers that can install the latest version.
Some GOG games provide recent patches additionally, so you can upgrade an old version to latest.

If you use GOG Galaxy, you will get the new version earlier, but offline installers will follow up soon, usually within one day.

The offline installer only offers the latest version, which is a very bad thing, because in cases where the latest version includes a game-breaking bug in it (i.e. Divinity Original Sin), then GOG gives you no possible way to download the non-bugged version.

Or with games like Chuchel that have been censored, GOG offers you no possible way to download the uncensored version.

To add more info:
https://www.gog.com/forum/general/provide_a_full_and_complete_changelogged_download_system

For OP, it varies between games. Some include hem, some have separate dlc installers. The exe and bins will be latest. Sometimes patches are provided.

If you just want the latest relevant stuff then gogrepo (use google search) is a script to download all offline installers and goodies.

You can roll back versions via Galaxy if you so choose.

Chuchel? Looked it up and apparently the main character design was changed. Huh.

I installed the release version which still had the original design so this was quite unexpected to hear.

Ah yes, only possible with the “optional” client though.

It is optional. You're not required to roll back your game. Or you can keep legacy installers on your PC if you had the game before newer versions rolled out. I have every version of The Witcher 3 released, by getting the original files and all the patches as they rolled out.

There are a very few games that are not fully up to date in the installers. For instance witcher 3 goty doesn't have the Chinese language patch 1.32 integrated into the installers. Dragonage Origins also has a patch that adds some bonus DLC and stuff that is an additional patch. Those are the only two that have "needed" patches that I know of.

There have been several threads about this recently. A recent one, the guy brought wizardry 8, downloaded the offline installer and it did not work on his windows 10. Now luckily, I hadn’t downloaded that update, so I ran the old one, not only did it work perfectly, it had additional content (pre made characters). I downloaded the one from the website, that ran through character setup, screeched through the sound card, didn’t have the pre made characters, and crashed at start up. So the installer available to him is broken, and there is no way of getting the old installer. So either he is forced to use the client or does not have a working copy. This is not “optional”. Sure, if you have been here a while and have old versions great. It’s irrelevant to wether or not the client is optional.

You can always request an older installer through support. They generally will provide it.

So I'd need to download dlc's, but not necessarily patches. Cool. Thanks for the info.