Nice article, Lindsay!
Just one thing — in your third eventuality a lot of “authors” would not be happy with having clips or excerpts of your writing for them shared without their express consent (and obviously sharing the whole piece without their permission is a total bad practice).
Also for case two. I’d be a little hesitant to work with a client that is using fake names to publish work under. Pseudonym-publishing is fine for authors, but I don’t think that businesses should generally be in the business of creating fictitious employees!
Mine are typically attributed to a point of contact at my client, given no byline at all (say a white paper) or attributed collectively to ‘staff’ or ‘[client] team’ as you write.
Good luck with your ghostwriting!