Many thanks to Felipe Ruan of Brock University for bringing to my attention the letters between cosmographer, and one-time editor of the crown-sponsored project of the edition of Isidore of Seville's complete works, Juan López de Velasco and the Mexico-based humanist Francisco Cervantes de Salazar, which I have just incorporated into the database. Even though López de Velasco's correspondence remains virtually unpublished to this day, references to many of the dozen or so letters presented here can be found in María Portuondo's "Secret Science" (Chicago, 2009). Several more are preserved in the Instituto Valencia de Don Juan in Madrid. In addition to that, Portuondo's mention of an exchange between Escorial architect Juan de Herrera and Velasco has led me to chase down and include two more letters from Herrera to Cristóbal de Salazar, secretary of the Spanish embassy in Venice, regarding the purchase of books for the library of the famous Royal Academy of Mathematics.