Museum conduct their own investigation
While responsibility for accurate reporting lay with the committee investigating Museum Acquisitions from 1933 onwards, museums conducted their own investigations. Museum staff were tasked with searching their registration systems and archives to form an initial selection of objects that might require further investigation. They excluded objects acquired before 1933 and those acquired after 1945, as well as those that had belonged to families for generations or with complete known provenance so that there was no question that they might have been wrongfully acquired.
Special emphasis in the investigation of the years 1933-1940 was placed on objects that had originated in Germany and after 1938 in Austria, and in the investigation of the years 1948-1954, a period in which many objects with problematic provenance came onto the market. Investigation of provenance of objects acquired after 1954 was more complicated. Large numbers of art works changed hands and it often proved difficult to establish whether the provenance was problematic or not. It was often impossible to trace the provenance of objects completely.
Supplementary inquiries were made at the art databank and library of the Netherlands Institute for Art History (RKD). Auction catalogues were a key source of information. The Netherlands Art Property Foundation (Stichting Nederlands Kunstbezit or SNK) and the National Archives also provided invaluable information. This secondary investigation required more expertise, for which the Museums Association (Museumvereniging) provided the necessary support. Although helpful documents and guidelines were published on the website, occasionally the support needed was in the actual investigative process. All this enabled investigators to form an overview of the objects of which the provenance may be doubtful. Every possible effort was made to trace the transactions and stories of these objects as fully as possible.