This is true.
And sometimes the question has to be asked several different ways, depending on the ethics and psychology of the TA-person/staffer/partner, etc. I remember one in which the "key" comprised these questions: "Do you have any other clients?" (which, of course, most do...), which netted a yes answer; so I asked, "Can you talk about their share structure, or would I have to call the company for all of them, too?"
Once she conceded she could talk about other companies, it was clear that the company in question had strapped on da gag...