Bottom line: whether or not any are/were prostitutes has no real bearing. An unwelcomed or forced interaction is still what it is; sexual assault and borderline rape.
Has there been any discussion of these ‘massage therapists’ former clients?
No. Nobody from the team seems to have spoken with anyone other than Watson's lawyers. They intentionally did not contact any of the women, and the women likely would not have shared info on past clientelle.
