[Campion]

Imagine Catholics not knowing for centuries that the "traditional Latin mass" was defined at the Council of Trent in the mid 16th century as a response to the Protestant Reformation.

All Trent did was codify and standardize the practice which had existed, almost unchanged, at Rome since the 5th century.

Mass done before that had many local variations (pre-Tridentine mass).

True, not all of which were abrogated by Trent. But if you compare, e.g., the Sarum Rite with the Tridentine, you'll find that they are very similar, with a few extra prayers, extra rituals, and extra rubrics in the Sarum rite.

[Tell It Right]

Look at all the changes in mass as it was noted by Justin Martyr (AD 2nd century) and Pope the Innocent (AD 5th century).

Then there are all the missals that was done away with at Trent. The only ones allowed to continue were the ones who could prove their missal was at least 200 years old.