Are papal writings valid? I don’t know what you mean by valid. Depending on the nature of the document, we must assent to varying degrees.
The Protestant Reformation did not reform the Catholic Church, so “reformatiion” is not the right word. It doesn’t mean that there was nothing bad happening in the Church. I am not knowledgeable about the issue of indulgences at that time, but that seems to have been the one thing Luther brought up which was in need of re-considering.
So I guess the COUNTER Reformation just happened by MAGIC er sumpin'; Right??