Absent from GR, GT, LU.
The long, beautiful and interesting melisma over "nomen" relates to the Evangelic account that Zacharia was cured of his 9-month God-given muteness when he was required to give his newborn son the proper name chosen by God.
The last words "iohannes erat" take the melody from the Alleluia response; however the last syllabe "erat" that would take the jubilus differs from the 4th neumatic element onwards, making it hard for the singers to "jump" to the response jubilus and finnish the verse from there; therefore perhaps the jubilus was not intended to be sung at the end of the verse.
This chant was also found with some minor differences in another cistercian source, and has been recorded by Ensemble Organum in "Chant Cistercian", Harmonia Mundi (HMX 2901392), 1999, 2nd track.