Zurich, 12 December 1955 - Institutional correspondence A letter from Klaus Herdeg to Willem Sandberg
May - July 1992 - Institutional correspondence Loaned works at the Museo Nacional Centro de Arte Reina Sofía in conjunction with the rearrangement of holdings between the Reina Sofía and Museo Nacional del Prado
New York, 14 August 1942 - Internal museum documents Elodie Courter Osborn's letter to Alfred H. Barr Jr.
New York, 20 August 1942 - Internal museum documents Elodie Courter Osborn's letter to Dorothy Dudley