[JdeBP]

> I'm still looking for how much of OS/2 made it into NT.

Very little, and the code re-use was pretty much nil.

The OS/2 subsystem in Windows NT only implemented the 16-bit OS/2 API. It only implemented the base CP API, not implementing the 16-bit Presentation Manager API at all, and not even implementing all of that base API.

Moreover, Cutler re-implemented the things needed by that API from scratch. He quite famously railed against the OS/2 mutex abstraction, naming his re-implementation in Windows NT a "mutant".