According to MACEY 1996, 171-73 and 208:
1st phrase of the hymn Ave maris stella (Cantus ID 008272) quoted in T1 (passage "gaude virgo salutata" ... end of folium):
The version of I-Mfd 1 is shorter than the one in I-Mfd 3 (the section starting with "Gaude virgo fruens delitiis" is missing). The motet is presented on two openings in the sources, connected by "custodes" and by the rubric "verte cito": in I-Mfd 1 the second opening starts with "Gaude mundi domina", in I-Mfd 3 with "Gaude virgo fruens delitiis".