You are right about the markings spreading and changing. But from what I've read and know about vitiligo (from books and people who have it), the pigmentation can and does come back. So a white patch can start having brown spots again. That's why you have to use the cream for the rest of your life.
In fact, I was watching a Lee Thomas interview, the newsman who has this disease and wrote a book) on YT yesterday where he pointed out some places that his pigment was coming back, just in that week.
Just wanted to say something in case somebody tries to pin you on that one little point-I admire your zeal for dealing with these morons. Clemente is a piece of work. I hope anyone considering him for employment takes a look at his Facebook page, or wherever he's posting this junk. What a fool.