The letter of August 1591, written from Cologne, is again addressed to Jan Moretus in Antwerp. The composer assured Moretus that the texts of the new chansons book which accompanied the letter, would not offend "les aureilles pudiques", and that the manuscript would only take

"peu de travail a les mettre au jour, [parce que les chansons] sont mis en bon ordre et bien correctement ecrites" (the manuscript would only take "little effort to publish them, because the chansons were put in the right order and correctly written").

Most presumably this concerned the manuscript of the Sonets, avec une chanson, ..., à deux parties. Livre second, composed for the daughters of Gillis Hooftman and published in 1592; De Castro mentions "deux Livres" (two part books?) containing twenty-eight "chansons courtes", a number corresponding exactly with the number of chanson parts in the printed edition. The sonnets are published by Phalèse, to whom Moretus again must have sent the manuscript for printing.

All this leads to the conclusion that the Officina Plantiniana was more than a mere sales point in Antwerp. The role played by Moretus in the publication career of De Castro, was actually that of an editor: the music manuscript was sent to him by the composer; he exercized moral authority over the content of the texts (unfortunately, we have no evidence that he also adjudged the music); he sent the manuscript to the printer (whose name appears on the title page of the printed volume; mostly Phalèse and Bellère, occasionally Bogard); and finally he oversaw (part of) the diffusion of the publication through the Plantin-bookshop

Note: Before 1589, when Moretus took over the business, Plantin may have played a similar role of editor of De Castro's music. However, since no correspondence seems to have been preserved between De Castro and Plantin, it is difficult to establish the actual influence of Plantin. The absence of such letters could be explained partly by the fact that De Castro himself was in Antwerp whenever a publication of Phalèse and Bellère or Jean Bogard was forthcoming, until just before 1589 when Plantin died. He could therefore negotiate with the office in person.