Merci Claude,
In the question is the the answer, I agree, logic would dictate that one or two of them will have to underperform, same is true of the Clyfford Stills at Sotheby’s, they can’t all make the money. Whenever multiple examples of a body of work by an artist are lumped in a single auction, there is the chance for opportunity. That being said, I think the Richter market is extra strong now, and I don’t see it softening much, so they’ll probably get them all off for good money, especially off the strong show at the Tate.