What's crazy about this is that it sounds like the people writing the code haven't got the slightest hope of even compiling it, let alone running it. They're just writing code, crossing their fingers, and committing it. It's a wonder the thing ever worked at all.
There’s a slide saying few developers could build a whole instance of win2000, but when working at this scale you rarely build everything from scratch locally. You work on your module and the build system will have to build everything nightly. I don’t read this as devs throwing completely unchecked code into source control.
Of course, things got better as time went on thanks to process improvement. I started in 1991, and I remember driving over to the NT team's building with a large (for the time) hard drive to grab a physical copy of the source tree. This was before NT was first released - when you tried running your build and went to shut it down, you had to watch the activity LED on the drive flash a few times to be sure the cache had synced to disk and powering down was safe. Fast forward a few years, and building all of WinNT was more routine, to the point it was just another component built by the automated VC++ checkin procedure (we called it submitting code to The Gauntlet), along with Excel and other Office components.
I might be misremembering if NT was part of Gauntlet, but it was definitely something we could and would build as desired.