Each time someone creates a written record of music, an editorial procedure occurs. This procedure could range from the regularization of minor notational nuances to the complete rewriting of the piece in accordance with the requirements of its current usage. To say, therefore, that Adémar de Chabannes edited the music he copied into Pa 1121, 909 and 1978 is unremarkable, for he was simply behaving as all writers of music have behaved before and since. What is remarkable is that we have a relatively complete record of the sources he would have had available to him when he produced these manuscripts. We are therefore in a singular position to gauge with some precision how Adémar went about editing as he copied.

Adémar's editorial method divides neatly between those pieces transmitted with text (tropes and prosae, for example) and those without (sequentiae). For most pieces in the former category, we are able to compare Adémar's neumations in Pa 1121 and 909 with the exemplar available to him during their production, Pa 1120. Where either or both of Pa 1121 and 909 disagree with Pa 1120, there can only be three possible explanations: (1) Adémar erred when he copied one or both of Pa 1121 and 909, (2) he perceived an error in Pa 1120 and corrected it in his manuscript versions, or (3) he understood the reading in Pa 1120 to be correct and consciously varied it.