In 1961, the Catholic Luther researcher Erwin Iserloh realized that in all the works and letters of the Reformer he nowhere explicitly mentioned nailing his 95 theses to the door on October 31, 1517. Philipp Melanchthon was the first to mention it in the preface to the first volume of Luther's Collected Works in 1546. But by then Luther was already dead. Melanchthon only came to Wittenberg in 1518, and so could not have been an eye-witness. So Iserloh concluded that the theses had never been nailed to the door, and began a huge debate, which has still not been brought to a final conclusion.
The unnoticed comment by Luther's secretary
In 2006, Martin Treu from the Luther Memorials Foundation of Saxony- Anhalt rediscovered a handwritten comment by Luther’s secretary Georg Rörer (1492-1557) in the Jena University and State Library, which although printed, had so far played no role in research. Right at the end of the desk copy for the revision of the New Testament in 1540, Rörer made the following note: „On the evening before All Saints’ Day in the year of our Lord 1517, theses about letters of indulgence were nailed to the doors of the Wittenberg churches by Doctor Martin Luther.”
The ultimate evidence has not been produced
Now Rörer was also not an eye-witness, but he was one of Luther's closest staff. The copy of the New Testament, in which he made his note, contains many entries in Luther’s own hand. The note right at the end of the volume leads us to assume that it was made at the conclusion of the revision work in November 1544. Directly beside it is another note, according to which Philipp Melanchthon arrived in Wittenberg on August 20, 1518, at ten o’ clock in the morning. This information is not to be found anywhere else and presumably came directly from Melanchthon himself. Rörer's reference to the Wittenberg churches in the plural must be emphasized, as it corresponds to the statutes of the university. According to these, all public announcements had to be nailed to the doors of the churches.
While this does not give final proof of the theses being nailed to the door, together with Rörer’s note it seems much more probable. It is at least so far the oldest source for it from the time when Luther was still alive. And: Wittenberg now has more than one “Theses Door”.
A complementary publication has been published, the anthology: Ott, Joachim/Treu, Martin (Hrsg.), "Luthers Thesenanschlag Faktum oder Fiktion" (Schriften der Stiftung Luthergedenkstätten in Sachsen-Anhalt 9), Leipzig 2008.