¶RTFM
While trying to find a way to set the frame rate on a WDM capture device in DirectShow and not have it just return S_OK and ignore my setting, I came across the following documentation in the DirectX 9.0c SDK for IAMVideoControl::GetFrameRateList():
Return Values
Returns an HRESULT value that depends on the implementation of the interface.
Whew, that's a relief. I thought it would return random values instead.
(It isn't easy to write documentation, and it's even harder when a technical writer who's not the API designer is doing it. However, some of the documentation in MSDN is downright silly.)