Labarte Organ Tablature
The Labarte Organ Tablature is a manuscript which was in the possession of Jules Labarte. In 1864, it was lost. However, around 1990 it reappeared in the Houghton Library at Harvard University.
The manuscript is dated to the 16th century and it contains three anonymous Alternatum organ masses.
References
"Labarte-Orgeltabulatur" in Beckmann, Klaus (editor), Repertorium Orgelmusik: Komponisten-Werke-Editionen 1150-2000, 57 Länder, Eine Auswahl. Third Edition. Mainz: Schott, 2001. Page 120