||Missa Sine Nomine
The manuscript is in: Biblioteca Vaticana, Chigiana Cod. C. VIII.
The work may be incomplete rather than being a missa brevis (which by tradition - a later tradition? - stops at the end of the Gloria in any case). Chorus also I assume? - Schissel (there is also a - more complete - Missa Sine Nomine by Ockeghem for 3 voices as well as this one for 5 voices - perhaps disambiguation is needed.)