Cotta Maximus, the younger son of Tibullus' patron Messalla, is prominently mentioned at xvi 41-44 as an unpublished poet of outstanding excellence. He is the recipient of six letters in the earlier books of the Ex Ponto. Syme finds it significant that there is no poem in EP IV addressed to Cotta: 'Ovid ... was now concentrating his efforts elsewhere: Germanicus, the friends of Germanicus, Sextus Pompeius ... The tardy tribute may perhaps be interpreted as a veiled reproach' (HO 128). But arguments from silence are dangerous; and Ovid's mention of Cotta seems flattering enough.
It is perhaps safer to postulate a change in Ovid's feelings towards his wife. She is never mentioned in EP IV, although she had been the recipient of some eight earlier letters from exile (Tr I vi, III iii, IV iii, V ii, xi, xiv, EP I iv, III i; Tr V v was written in honour of her birthday). At EP III vii 11-12 Ovid indicates that his wife's efforts on his behalf had not matched his hopes:
nec grauis uxori dicar, quae scilicet in me
quam proba tam timida est experiensque parum.
The fact that Ovid chose not to address any verse epistle to his wife during his final years at Tomis may well reflect a cooling in his attitude towards her.
Differences between Ex Ponto IV and the earlier poetry from exile
The criticism most often made of Ovid's poems from exile is that they are repetitive and therefore monotonous. EP III ix 1-4 shows that the same criticism was made while Ovid was still alive:
Quod sit in his eadem sententia, Brute, libellis,
carmina nescio quem carpere nostra refers:
nil nisi me terra fruar ut propiore rogare,
et quam sim denso cinctus ab hoste loqui.
Ovid does not attempt to deny the criticism, but explains that he wished to obtain the assistance of as many people as possible:
et tamen haec eadem cum sint, non scripsimus isdem,
unaque per plures uox mea temptat opem.
(41-42)