I've just got my hands on a copy of Codex 10784 from the Österreichische Nationalbibliothek, which does not appear in any of the standard fencing bibliographies. It is a handwritten work in Italian by Giovanni Battista Maffani of Perugia, entitled “Compendio e discorso di tutto quello, in che consiste la virtù delle spada”, the dedication dating it to 1629 in Vienna.
It is dedicated to Maffani's patron, Archduke Wilhelm Leopold (the youngest son of Holy Roman Emperor Frederick II) who went on to hold a variety of offices, not least governor of the Spanish Netherlands.
Interestingly like Capoferro, Maffani describes himself as "master of the glorious German nation", stating that before coming into Leopold's service he taught in his home-town of Perugia, in Siena (like Capoferro) and in Germany. Perugia and Siena have in common that they were both university towns with large numbers of German students, who likely provided a significant source of patronage for both masters.
The treatise itself is perhaps 25,000 words, divided into 91 chapters. There are no illustrations, except for one simple footwork diagram, with no detailed expositions of individual techniques. Instead the work reads like an extended "theory" section, such as that found at the beginning of Capoferro or Alfieri for example, covering principles, specific tactical and situational advice, as well as sundry matters such as salle etiquette, the various tempers of a sword and so forth. Maffani treats on the single rapier and briefly on the rapier and dagger. He covers the standard four rapier guards, referring intriguingly to a fifth guard "in the manner of a Saracen" and to a hanging guard with the point directly downwards (which he seeks to discourage).
While its emphasis on principles over specific techniques might limit its usefulness as a stand-alone text, it fits squarely into the tradition of contemporary Italian rapier, giving context and nuance to our understanding of early 17th Century Italian swordsmanship.
If there's sufficient interest a transcription in collaboration with Steve Reich is a distinct possibility in the medium term.