That was no formal canon of Scripture prior to Trent is an old Protestant canard. The canon was set in 381 and affirmed when St. Jerome was commissioned to produce a Latin Vulgate translation of it. It was re-affirmed at Trent in response to the Reformation's challenge to it and the removal of books previously canonized. The canard has been propagated to give cover and credibility to the Protestant canon.
Let's agree that we can have different theologies, interpretations and doctrines, but matters of documented history are not subject to convenient revision.
That was no formal canon of Scripture prior to Trent is an old Protestant canard.
Rather, that Rome had an "infallible, indisputable settled canon before 1546 (the year Luther died) is an oft-repeated Catholic canard. And one that i have often corrected here (and here here, here and here etc.) on FR.
See here, for the facts are that there was dispute over book s right into Trent (which some argue appears to differs as regards 1 + 2 Esdras with its confusing nomenclature), which finally definitively settled the matter of the Old Testament Canon, and affirmed the Vulgate (but which required a thorough revision, as there was not a single authoritative edition at that time, of there there were many variant editions, with the oldest extant manuscript containing the Epistle to the Laodiceans. More below.*) Some Roman Catholics even held that the Vulgate was superior to the Greek in the places where they disagreed!
*The affirmation of Trent necessitated an official version which resulted in the Sistine Vulgate , undertaken by the over zealous Pope Sixtus V, with at least two assistants, and for which Vulgate he wrote the Bull Aeternus Ille (1 March 1590), which was attached to the Lateran basilica, which declared it to be the the authorized Vulgate of the Tridentine Council, and excommunicated those who deviated from it. But it is understood that this Vulgate was not to be reprinted for 10 years outside the Vatican (though it was found in many countries, and the pope sent one to the king of Spain), and it is contended that the Bull was not properly formally promulgated. Bellarmine warned of the danger of this Vulgate and Bull to the claims of the church, and after the sudden death of Sixtus (who had placed one of Bellarmine's books on the list of forbidden books), further sale of the Sistine Vulgate was forbade, and Bellarmine recommend buying up all the copies (over 40), which the succeeding pope Clement 8 executed, repurchases being mostly from Germany, Belgium and Holland.
Correction of its many errors resulted in the first edition of the Clementine Vulgate (official version till 1979), presented as a Sixtine edition, with a preface in which Bellarmine charitably attributed the problem of the previous version to being that of copyist errors, rather than being the fault of Sixtus. And which removed 3 and 4 Esdras and the Prayer of Manasses (commonly found in medieval MSS of the Vulgate, immediately after 2Chronicles) from the Old Testament and placed them as Apocrypha into an appendix following the New Testament. and the Vetus Latina (not really a single version) the current Nova Vulgata which is said to follow the Hebrew and Greek textual variations more often than the Latin ones.
Other sources: The American ecclesiastical review;: a monthly publication for the ...: Volume 51 - Page 492-94, and Vol. 46, pp. 387-390Catholic University of America
The Catholic faith; or, Doctrines of the Church of Rome contrary to ... By John Harvey Treat, p. 542
Bruce M. Metzger, The Early Versions of the New Testament, Clarendon Press, Oxford 1977, pp. 348-349