Here is another excerpt from the Jerome Biblical Commentary on the canon decision at Trent. This touches on the inconsistency of using "historical church usage" as a method for determining the canon at Trent.
Even at Trent, however, the Council Fathers did not specifically attempt to press the detail of Church usage back beyond the period of Jerome, for the used the Vulgate as the norm for Church usage, condemning “anyone who does not accept these books in their entirety, with all their parts, according to the text usually read in the Catholic Church and as they are in the ancient Latin Vulgate”. There are many difficulties here that demand investigation. First, in the period before the Vulgate there was no consistent Church usage, as we have seen. Ironically, Jerome, the translator of the Vulgate, was very clear in his preference for the same short canon that Trent rejected in the name of the Vulgate. The Vulgate was introduced into the West over many protests (including that of Augustine) asserting that Jerome’s translation from the Hebrew was an innovation against the Church’s usage of translating form the LXX. Second, from Jerome's time on, the Vulgate has not been a perfect witness of Church usage, for it was several centuries before the Vulgate won acceptance in the Church. And even then, the Vulgate was a norm only in the Western church usage. Although Trent was an ecumenical council, the constituency of the Fathers was Western; and perhaps insufficient attention was given to the usage of the Eastern Churches. Third, if Church usage was the norm for selecting the books of the canon, then several books that had been used in the Church were omitted. For instance, 1 Esdras was used by the Fathers more than was canonical Ezr/Neh, and the requiem liturgy cites 2 Esdras. Copies of the Vulgate often contained 1-2 Esdras and the Prayer of Manasseh – books not accepted at Trent. (pg 523-524)
More on the Esdras confusion in the future.