This is a "Riddle Canon". 7 notes of Tenor(2) part(C-E-C-D-D-G-E) mean vowels of "Vive le roy".
C -> U
E -> I
C -> U
D -> E
D -> (L)E
G -> (R)O
E -> Y (= I )
"Le Roi Est Mort, Vive Le Roi !" = "The king is dead, long live the king !"
Josquin des Pres was born in c. 1455 and died in 1521
Canti C was published in 1504
1483 Louis XI -> Charles VIII
1498 Charles VIII -> Louis XII