I've did a compete namespace and had the same issues. MS only documented at all after being taken to court by the EU. The docs are barely enough and new interfaces have been added since XP, and not all of them documented. Many don't even have a name you can get at, let alone a interface definition, just a GUID. Some, others have worked out, some, no one outside Microsoft knows.
My eyes are now open to this crap way of working. The "magic blackbox" thinkings are naive if they think documenting the surface of the blackboxs are enough. The more complex the thing, the less well documentation is going to be able to cover all the combinations. I'm not saying source instead of docs, I'm saying source as a fall back for when the docs are not enough.