La Trobe University - Library: Medieval Music Database - Browse By Composer - Annual cycle of feasts of liturgical chant, liturgical polyphony and secular music of the late middle ages.

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Manuscripts containing works by Byttering

Aosta, Biblioteca del Seminario Maggiore A1 D19 - not catalogued here.
London, British Library, Additional 57950 (olim Old Hall, Library of St. Edmund's College)
York, Borthwick Institute of Historical Research 2