What about Huss and Wycliff? They were before Luther, too. Luther said, "I have taught and held all the teachings of John Huss, but thus far did not know it. In short we all are Hussites and did not know it!"
The problem with the canonization process is they are considering all sorts of people these days including Martin Luther of all people. //eyes rolling//
But if your infallible pope proclaims him a Saint, you must accept it. And there was a Catholic/Lutheran accord signed in 1998 regarding a common view of salvation by grace. Hmm...
The plus side of papal infallibility, of course, is that the Vatican supported the South in the Civil War ;-)