You are all correct, and not going insane after all! There seems to be a bug currently affecting all downloads of AppId 90 for Windows-based installations.
This bug is not the same as other previously described bug which could be fixed by using beta string, or several retries with steamcmd.
Specifically, the bug affects DepotId 5, which is the Windows Dedicated Server files
Basically, nobody can download files for this depot (regardless if you use Steam, steamcmd, or third-party tools like steamCooker's TinCFT)
From what I can see, this affects all users, including anonymous user as well as users who have already purchased goldsrc games on their account...
I have reported this via Steam forums for Bug reports:
Also via Steam support Ticket:
In the meanwhile, I have managed to reconstruct the missing files for this depot (with exception of hltv.pdb, which is not essential for operation anyway). All files pass checksums for latest manifest, so are up to date. Feel free to download from my github repo here: https://github.com/fragtion/SteamApp...cated%20Server
Basically you will just install AppId 90 with steamcmd as normal, and then incorporate the missing files from the github repo, and then you will have a functional instance of the latest hlds base for windows (Build '8308') ready to use and apply your addons etc.