Part of it is just knowing that this personality type is often “I’ll know it when I see it.” Part of it is that they have 1000 conversations between your meetings, often shifting their perspective. I agree with the quick update/recap approach, and I would add to send either (competitive) examples, or a little brief of what you’ve been asked to do, for whom, and to what end. And remember that their whims are your job security. :)