Flushing, New York, 23 May 1939 - Institutional correspondence Simon Guggenheim's and Dana C. Backus's form letter to ask for donations
New York, 28 April 1977 - Internal institutional documents Conversation between José Mario Armero and William Rubin
Madrid, 17 September 1980 - Institutional correspondence A letter from José Mario Armero to Íñigo Cavero