Since there were no offical statements from the RCC on justification, you can wiggle all around to deny the obvious that Rome's theologians had very different opinions on justification.On the contrary, an "official statement" (by which presumably the author means a dogmatic declaration) is not required in order for clarity about a matter to exist.
A trivial example: there is no dogmatic declaration (on the order of a Pastor aeternus or Munificentissimus Deus) that murder is a grave sin. Nor is one needed.
A more relevant example would be the circumstances prior to Nicaea. The fact that there was no Nicene Creed, and the fact that no "official statement" about the Holy Trinity had been promulgated, do not mean that there was no certainty about the Trinity prior to Nicaea. The purpose of Councils isn't merely to define what must be believed (although that would be sufficient in my book), but rather to address issues related to faith and morals that have become sufficiently controverted due to errors being taught by some in the Church as to warrant an "official statement". So if no "official statement" concerning justification existed prior to Trent, it is no measure of whether there was any uncertainty or ambiguity about what the orthodox doctrine was, just as there was no serious uncertainty concerning the Trinity prior to Nicaea and the rise of Arius.
It's a straw man to suggest that we Catholics must have a dogmatic declaration of literally everything we believe - a straw man that is propped up in order to suggest that we suffer from the same formal doctrinal confusion as Protestants. It is a crude sort of tu quoque, by which the Protestant hopes to blunt the perfectly valid criticism of Protestantism that there is no reliable means among them by which they may objectively know the truth.