In his remarks in defense of the Old Latin version (Comm. Rom 5:14), Ambrosiaster names three third-century Latin writers — Tertullian (d. 215), Cyprian (d. 258), and Victorinus (d. 304) — whose scriptural citations offer in his view an authoritative basis for the “true” text (hoc autem verum arbitror). For Ambrosiaster, these writers are ancient enough to have escaped the corrupting influence of the great controversies of the fourth century.
But who might be missing from this list of authorities?
Of course, Ambrosiaster makes no claim to identify all of the writers whose citations he considers authoritative. Certainly, the inclusion of Tertullian is remarkable given his association with the Montanist heresy. Yet the omission of the schismatic Novatian makes perfect sense. Otherwise we see no conspicuous absences among named Latin writers of equivalent antiquity who can claim any significant body of citations, unless that is, we consider the Latin translation of Irenaeus’ Adversus haereses.
Indeed, given Irenaeus’ antiquity, reputation for orthodoxy, and evident qualifications as an authority on scriptural matters, it is noteworthy that Ambrosiaster does not seem to know of a Latin translation of Irenaeus. At the same time, between Commentarius in epistulas Paulinas and Quaestiones Veteris et Novi Testamenti, Ambrosiaster refers to Irenaeus eleven times, but to Tertullian only five times, Victorinus twice, and Cyprian just once (all are allusions). So it appears Ambrosiaster does consider Irenaeus an authority on other matters, yet he is silent on Irenaeus’ text.
Of course, a good explanation would be that when Ambrosiaster wrote (perhaps in the mid-380’s) Adversus haereses had not yet been translated into Latin. (We might consider that Gryson et al. date the translation to 380–395.) But given that the Latin translation of this important second-century work supplies such a rich source of early so-called “Western” readings, including many that are unattested in Greek (such as Mark 16:19 at Haer. 3.10.6, attesting part of the Markan long ending), the later date increases the likelihood that such readings may reflect fourth-century influences on the Latin translation rather than the initial Greek text.
 R. Gryson, B. Fischer, H. J. Frede; Répertoire général des auteurs ecclésiastiques latins de l’antiquité et du haut Moyen Âge (2007) 2:594.