The Journaux of the Plantin Bookshop, which can now be consulted at the Plantin-Moretus Museum in Antwerp, present a day-by-day account of books bought and sold by the Officina Plantiniana. At best, the entries include the date, the supplier or client, their profession or occupation and/or origin, the title of the work, the number of copies purchased or sold, and the price of the transaction. Because of their unique character, the Journaux represent exceptionally valuable evidence of the contemporary reception of polyphony and the diffusion of polyphonic music prints accross Europe and the role played in this process by Plantin and Moretus.
Starting from these Journaux a survey could be made of all the music books traded in the shop of the Plantin firm in the last decades of the 16th century, which enabled us to compare the sale of the music of many polyphonists. The results of this comparison, which can be read in Table V, are quite surprising. De Castro, who after all is at present relatively unknown, headed the field and was followed at a modest distance by the widely-recognized master, Orlandus Lassus.
The Journaux also allow to acquire insight in the diffusion of De Castro's music. Booksellers in the German Empire, France, the Low Countries and England bought De Castro's books in theOfficina Plantiniana to resell them locally (see Table VI, in which a comparison is made with the diffusion of Lassus' music by Plantin and Moretus).
The table shows that, although Lassus' music was still much more widely diffused, De Castro's music seems to have been bought more frequently and regularly by the same booksellers. For instance, François Boulet from Lille purchased only a Magnificat book and two volumes of bicinia by Lassus, whilst he bought copies of six different volumes of music by De Castro. Nicolas Claudet from Pont-à-Mousson (Southern France) obtained copies of no less than seven different titles of De Castro, whilst he request a copy of Lassus' best-seller, the Fleur des chansons only twice. Bernard Wolters from Cologne became an advocate of De Castro's music in the last two years of the century, ordering copies of at least five of the later Phalèse and the Grevenbruch publications, whilst desiring only a few copies of Lassus' La fleur des chansons. Thus, as far as the sale through the Plantin bookshop may be generalized, many more people owned a volume of Lassus' music than of De Castro's, but it seems that once a client had bought music by De Castro, he wanted more.
The huge success De Castro enjoyed amongst his contemporaries makes it difficult to comprehend fully the reasons behind the oblivion into which this composer and his music would pass during the centuries that followed.