A summary of the major manuscripts of Pliny the Younger's letters.
L.D. Reynolds, Texts and Transmission: A Survey of the Latin Classics, (Oxford: Clarendon Press, 1983), 316-322
In 1502 Avantius published in Venice an edition (A) of the latter part of Book 10, letters 41-121. He tells us that they had been discovered in France by one Petrus Leander. The letters were numbered xvii-lxxiii, and so they appear in Avantius's edition. If their source, as seems likely, was Π [the complete set of Pliny's letters], then someone must have been very careless to have so promptly mislaid forty letters. His edition was reprinted by Beroaldus (Bologna, 1502/3) and Catanacus (Milan, 1506/7).