Using the poems of John Scottus Eriugena as a case study, the author aims to show that glossaries that preserve the lemmata and glosses of a text in the same order as that of a codex unicus of the work can be used to construct the common exemplar from which the entries of the glossary and the text of the codex unicus derive. Thus, at least for Medieval Latin texts, glosses can be an essential component of the recensio codicum. The author argues further that where a dating order of poems can be established (as in the case under consideration), such constitutes evidence of editorial management on the part of the author or an associate.