I did a bunch of research on the Latin Vulgate, and found out that it kind of never existed, and that solved the problem of Trent's declaration of the Vulgate as "THE" version. To explain, the texts of the Latin bibles all across Europe were a mix of the Older Latin translations and Jerome's version. After a while they ended up getting mixed together in the copying depending on a certain passage and the preference of the local bishop, etc. It's like today when people memorize verses in the King James and use that wording alot and it becomes familiar, even though everyone else is reading the NIV or ESV (or if they're like me NRSV).
So basically by that point, they knew from the Greek where the errors were (like Gen 3:15) and corrected them in several reform movements throughout the middle ages, but some errors still persisted. The problem was that Erasmus' Greek ALSO had errors in it, so there wasn't a clear solution.
So Trent did what Catholics always do: revert to Tradition. So based on the authority of St. Jerome, they declared his Vulgate to be the best version, even though no one really knew which one it was hah. BUT the Clementine Vulgate was an accurate corrected addition that flourished for a long time after. So while the Reformers were criticizing the Vulgate and adding their "alones" to the Vernacular bibles, and removing books from the canon, the Catholic Church was just revising the Vulgate, or if you like: always reforming, by continually evaluating the Latin text.