The tendency to secrecy and falsification of dates casts doubts about the authenticity of many primary sources. Several historians have hypothesized that John II may have known of the existence of Brazil and North America as early as 1480, thus explaining his wish in 1494 at the signing of the Treaty of Tordesillas, to push the line of influence further west. Many historians suspect that the real documents would have been placed in the Library of Lisbon. Unfortunately, a fire following the 1755 Lisbon earthquake destroyed nearly all of the library's records, but an extra copy available in Goa was transferred to Lisbon's Tower of Tombo, during the following 100 years. The Corpo Cronológico (Chronological Corpus), a collection of manuscripts on the Portuguese explorations and discoveries in Africa, Asia and Latin America, was inscribed on UNESCO's Memory of the World Register in 2007 in recognition of its historical value "for acquiring knowledge of the political, diplomatic, military, economic and religious history of numerous countries at the time of the Portuguese Discoveries."