It's been a long time since I read it as well and I knew the hardware/microcode people in the book better than the OS folks--and I think the book probably focused on them more. Maybe it's not really SWE lessons per se as so much as just a really good account of a computer systems project. (I worked at Data General for many years though I joined a few years after the events of the book.)

Showstopper (about the development of Windows NT) is more focused on software obviously.