So I'm updating to 1.02 right now and it says 12 gigabytes!? Is the whole game being redownloaded? Also the update hasn't been made available in the offline files, please fix that.

I guess because basically all the game is contained in two massive .pak files, any changes in game could would mean a re-download of these files.

Not sure if GOG has partial downloading of files like Steam has.

Yeah, I think it is problematic for people with limited bandwidth, thankfully not for me but for some this is a big problem.

I encountered the same thing through GOG Galaxy. However I initially downloaded the PD v1.0 through the GOG Download tool. When I donwloaded the 1.01 and 1.02 patches (59 mb and 101 mb) they came in the form of 32 bit where as v 1.0 was 64 bit. There was an issue updating from those patch files.

setup_phantom_doctrine_1.0_(64bit)_(22960)

patch_phantom_doctrine_1.0_(22960)_to_1.0.1_(23003)

patch_phantom_doctrine_1.0.1_(23003)_to_1.0.2_(23026)

patch log

Error modifying C:\GOG Games\Phantom Doctrine\IWTB\Binaries\Win64\IWTB-Win64-Shipping.exe
Error modifying C:\GOG Games\Phantom Doctrine\IWTB\Binaries\Win64\IWTB-Win64-Shipping.pdb
Error modifying C:\GOG Games\Phantom Doctrine\IWTB\Content\Paks\pakchunk0-WindowsNoEditor.pak
Error modifying C:\GOG Games\Phantom Doctrine\IWTB\Content\Paks\pakchunk1-WindowsNoEditor.pak

Makes me glad I don't use Galaxy. Using the offline installers from your account page (via GOG web) results in MUCH smaller files in this case, and you can keep them to revert back to if necessary.

Definitely - from what I gather Steam manages to (most of the time) handle patching better than Galaxy.

It doesn't make sense that a platform specifically designed to facilitate automated patching (among other things) does it much more inefficiently (in terms of bandwidth) than grabbing the individual patch installers.

And it's also strange that the manual downloads and the Galaxy downloads appear to not reuse each other's resources - I get they're almost certainly being built by different teams, but surely they can communicate once in a while and get on the same page once in a while?

Depends on the game. ARK: Survival Evolved needs to download the whole file, no matter the size, even if you make a one character change.