“Poland still lacks a viable procedure for processing restitution claims from Holocaust victims both within the country and from abroad,” Ms. Grimsted wrote in an article to be published in the International Journal of Cultural Property.

In response to questions from The New York Times, curators at the Gdansk museum acknowledged that six other paintings in their collections are also identified on the Origins Unknown Agency’s list of missing Dutch works thought to be in Poland.

In addition to the van Goyen, the art includes paintings attributed to Pieter de Hooch and Ferdinand Bol. One of the works, by Jacob van Ruysdael, was taken from a Jewish publisher in Berlin, German researchers found, and ended up in the hands of Dutch art dealers who appear to have sold it to the museum in Gdansk.

Willi Drost, the director of the Gdansk art museum during the war, was an avid buyer of Dutch old master paintings, according to the Origins Unknown Agency report.

Magda Mielnik, curator of the historical art department at the Gdansk museum, said she and her colleagues are working to document the history and provenance of the collection with a plan to publish a book about all the works next year. “The paintings looted from the Netherlands are an important part of our research,” she said.

Frank Lord, a New York-based lawyer for the Goudstikker heirs, said the family believes two works in the museum are from the Dutch art dealer’s collection. He declined to discuss any plans to seek their return.