How to weigh up the contradictory evidence of the manuscripts? Dolveck’s reconstruction of the tradition is essentially bipartite, with the above-mentioned family, known as α, on the one side, and the remaining manuscripts (for the letters) divided into several subgroups on the other side (δ). See the following simplified stemma, containing both the manuscripts that Dolveck recommends using and those which have been used by previous editors, based on one drawn by Giulia Marolla:*
There are then two possibilities: one is that Dolveck’s reconstruction of the tradition is at error at this point, the other (more likely) is the presence of contamination. Although contamination is not otherwise visible between the α family and ν, one point that is worth making is that it might happen more easily with the address formulae, ‘Sidonius greets his friend x’, than with other parts of the text. Sometimes scribes left these greetings unfinished to be completed later by the rubricator (this is the case, for example, with Parisinus Latinus 2782, a descendent of ν on which the name is left out but the reminder to the rubricator appears in small writing on the very edge of the page). If it was decided to fill in an unrubricated copy that did not have such a note, and a copy that was not the original exemplar happened to be available, you would have the capacity for the name Syagrius to be introduced from the α-family.
If the supposition of contamination is right, we are left with two different names on the two sides of a bipartite tradition. How to decide?
First, onomastics. The name Sagittarius (archer) is certainly not impossible, but there is not another one attested in either of the first two volumes of PLRE, and I have not found it epigraphically: it appears only as a description of archers in the army (and there not a name) or as a sign of the Zodiac. But it does appear a century after Sidonius, for an obnoxious and militaristic bishop of Gap described by Gregory of Tours. Syagrius is not a common name but it was the name of two consuls in 381 and 382, of a correspondent of Sidonius (Ep. 5.5 and 8.8) descended from one of them, and of a warlord in northern Gaul in the same period. Could this be Sidonius’ friend addressed in the two later letters? The addressee of letter 2.4 is certainly important enough to be the noble Syagrius (there’s reference to the celeberrimam disciplinam of his house). We have learned from Joop van Waarden to be alert to the various pronouns used in Sidonius’ letters, not as a direct equivalent of the tu vos distinction of later Romance languages but as something rather more subtle and complex: in this context we should note that, as with Syagrius, Sidonius uses the tu form for the addressee of 2.4, and though the letter does not seem to exhibit as much familiarity as the other two, that could be attributed to the genre of the recommendation letter. One might wonder if the addressee does not feel older than Syagrius – particularly as the letters in book two tend to be earlier than those in the later books – but it would not actually be surprising if a younger aristocrat were placed in a position akin to guardianship, since he had more chance of living longer to carry out his role.
And which was likelier to be corrupted into the other? Any reader of Sidonius will come across the name Syagrius, referring either to his friend (Ep. 5.5, 8.8) or to the friend’s distinguished great grandfather (Ep. 1.7.4, 5.17.4, 7.12.1). One of those mentions had already occurred in the previous book, so it is not impossible that it might have sprung to a scribe’s mind in conscious or unconscious response to a name that looked like a description rather than a name. On the other hand, one might think that it was likelier for the unusual name to be corrupted into a not uncommon noun: could Siagrius have been misread as an abbreviation Sag’arius?
I don’t have a solution to this onomastic and textual problem (though you may guess that I tip slightly towards Syagrius). But I do think that (for example) the entries for both Syagrius and Sagittarius in PLRE and similar standard works should have mentioned the sheer uncertainty. We need to look at critical apparatuses, and they need in turn to be reliable.
*I do not give manuscript sigla here, but they are all standard ones except that: V = Vat. Lat. 1661 (and not Vat. Lat. 1783 , here Vt); S = Paris, IRHT Collection Privée 347 (ex-Schøyen collection), B = London, BL, Royal 4 B. IV, Leip = Leipzig, UB Rep. I 48