Johannes Ockeghem’s Missa Prolationum is a well-known specimen of fifteenth-century notational complexity. As it is notated in the Chigi Codex, it consists entirely of mensuration canons. However, the other complete manuscript copy of the piece, in the manuscript Vienna 11883, eschews this complexity in favor of resolved notations ( resolutiones ) with uniform mensurations. Reexamining these resolutiones in light of generic mensural norms, statistical analysis of the work’s metrical structure, and subtle notational correspondences between the two manuscript copies suggests that the resolved notations in the Vienna manuscript are the result of a productive, formalist music-analytic encounter between their creator and the Missa Prolationum . Seen in this light, these resolutiones offer a new perspective on the early reception of this music.