I don't have a clear picture of the split myself but it seems to me
that docs.python.org should be the master reference data for
*distutils*. That's somewhat screwed, though, as we're recommending
use of setuptools, and setuptools messes round so invasively with
distutils that the usefulness of pure distutils documentation is
limited :-(

docs.python.org should provide a distutils reference, and drop the "Installing/Distributing Python Modules" guides in deference to the PUG.

and setuptools (as an extension of distutils) should provide a *complete* index of commands/options that covers everything, not just what it changed or added, because it's too hard for users to keep track of what's pure vs modified. That's my plan in the refactor of the setuptools docs I'm working on.