From the New York Times’s account of the latest restitution case, the matter hinges on whether the significant profit made on the work’s resale is evidence that the original sale was made under duress. Hugo Perls and Paul Rosenberg bought the work for $13,200 in 1938. Eventually they sold it through New York’s Knoedler for $22,500. That 70% appreciation looks like a windfall. In the art market, resale margins are often much higher than that even today.

In a statement, the Met strenuously denied there were grounds for the claim, asserting that the 1938 sale had been for fair market value and had not been made under duress. The amount the Leffmanns received was, the museum said, “a higher price than any other early Picasso sold by a collector to a dealer during the 1930s.” The Met said its ownership had never been questioned until Laurel Zuckerman, administrator of the Leffmann estate and great-grandniece of Paul and Alice Leffmann, approached the museum more than 10 years ago.

The museum also said the Leffmanns had made no claim on the painting after the war, when they did try to reclaim property they had been forced to sell.

Met Picasso Belonged to Family That Fled Nazis, Suit Says  (The New York Times)