I finally downloaded all of Fallout 4's offline bin files after a week and now it wont install! One (or several, or all) of the files are apparently corrupted! How do I run an integrity check to know what files to download? I've never had this problem before. It took me forever to download on my crappy internet, so this is very maddening.

If the installation can't process because of some install offline files, it is suppose to tell which ones are to be downloaded again. But as neumi5694 says, it is an option to select before the install and the integrity check lauch before the installation (you can't just check integrity, you have to lauch the installation for the integrity check to proceed).
I sympathize as I also spend a lot of time downloading dozen and dozen of files for big games with a poor internet connection...

Out of curiosity, was it bin-1 that was corrupted for you? That one downloaded corrupted twice for me, and since it was the ecact same (smaller) size both times I have to assume it's corrupted on their end due to the issues they're having currently.

It is too small indeed, was so from the beginning.
Funny enough, I was just able to install the game - including integrity check. Might not work for all languages tho.

No issues with running the integrity check nor the installation of the English version here either.
The 1st bin file having a slightly smaller size compared to the rest of the packages is normal, always was. Check some of the other titles in your library with more than two bins.

It was bin-1. I assume their servers might be having problems since a high profile game just released.

I ended up installing it using the corrupted bin-1, then used Galaxy to do a repair on the bad files. 160 mb download instead of 4gb again that way.

On a bunch of single installer exe's i don't see the option. Though i recall seeing it in the past, especially ones that exceed 4Gb and multiple bin files.

Though my own opinion, the installer and archive isn't very robust.

I was testing to see if i could change the size of the installer bins to more or fewer to better utilize space for CD's/DVD's. So i tried splitting and joining the files (the 7z archiving doesn't really care), and GoG's files expects a certain number of files at a certain size, and then those files of certain hashes. Anything else and it complains and refuses to work.

Can you name some? I didn't really pay attention, but I don't remember this option missing. Maybe it's some of the old pre-Galaxy installers?

Could be. Pulling up Albion the file is 2.0.0.3 dated 2016.

Though downloading the updated 1.38 albion, i still don't see the option for integrity checks.

Others included Aquaria, bastion, bioforge, braid....

It's possible it runs a hash on the exe file before getting to the installer (which would explain the delay over NAS/Network activation rather than instant opening). Or maybe it's considered too small to worry about and will barf during install if there's an issue.

There's nothing in the 'help' options that comes up when you put in /? when running the file from the command-line, i half expected a /Integrity or /Verify; but i didn't see it.