[Curtis 1979b]: 'Tenor part of a setting composed by Dufay early in his career. This version shows striking differences from the more normal one, however, the most remarkable of which is the manner in which the symmetry of the phrase structure of the latter has been completely sabotaged. [...] The purpose of the inclusion of this vocal part is by no means clear [...], though it may have been intended as a basis for polyphonic improvisation.'

[Hamm 1964] places the Kyrie between ca. 1415 and 1429