Or just making it up out of whole cloth, whichever suits your fancy.
Given that Luther was rejecting it 40-50 years before, how do you suppose that's possible? Did Trent have a "wayback" machine to go back to 1500 and inject their invented ideas into Catholic Europe (while everyone was anesthetized, no doubt)?
The Council of Florence actually said more about purgatory than Trent did ... over 100 years earlier.
As Campion noted "Luther was rejecting it 40-50 years before". And, speaking of Luther ....
In his personal translation of the New Testament into German, Martin Luther inserted the word allein ["alone"], though he knew it to be absent from the Greek text. When he was rebuked for having done so, he retorted, "If your Papist [i.e., Catholic] annoys you with the word [alone, as added to Rom. 3:28], tell him straightway: 'Dr. Martin Luther will have it so. Papist and ass are one and the same thing. Whoever will not have my translation, let him give it the go-by: the devil's thanks to him who censures it without my will and knowledge. Luther will have it so, and he is a doctor [i.e., teacher] above all the doctors in Popedom.'"
Now there's a thread that slipped by the Protestant freepers, unnoticed.