Some are, some are not. Some are so bad it's unfunny. Literally someone has read the COM IDL and made up some padding. The core protocols like MSRPC are poorly documented i.e. the interoperability specs. They definitely have more than one person (did I suggest otherwise?) but I suspect the documentation was outsourced for a lot of stuff to people who have no idea how it works
Anecdotal, but sometimes things seem so dysfunctional within MS that I can't believe they get anything done at all: I once met a professor at a conference who said his grad students were reverse-engineering some of Microsoft's distributed system protocols (not MSRPC). I asked him why he didn't directly contact the team owning that project at Microsoft for help instead, and if I should introduce him to them -- I had met them before and they were pretty friendly and eager to get people to use their stuff. He said he was doing the reverse engineering for Microsoft. When I was like "WTF, why?!", he wouldn't give any details but said in an offhand way that MS needed somebody to document the system.
Now, I cannot imagine what unearthly sequence of events led to a snafu where MS had to ask an outside party to reverse engineer their own stuff in order to document it... But that may explain your experience.
