"The 31-Line Indulgence Provides the Earliest Precise Date for European Typography"

Between 1454 and 1455 Johannes Gutenberg printed at least seven different dated issues of an Indulgentia (Papal Letter of Indulgence) issued by Paulinus Chappe for contributions to the war against the Turks. Remarkably 46 copies of the 31-line Indulgence survived. The earliest date on any of these copies is October 22, 1454. Other surviving copies are dated from 25 October 1454 to 30 April 1455. For an ephemeral item printed at this extremely early date in the history of printing by movable type in Europe, that is a remarkable number of copies. Most probably the relatively large number is reflective of the large numbers of the indulgences that were printed and sold. ISTC No. ic00422600  showed the availability of a number of different issues in digital facsimile.

"The so-called 31-line Indulgence provides the earliest precise date for European typography. Its text is a plenary indulgence granted by Nicholas V for contributors to the defense of Cyprus against Turkish siege. The text leaves blank spaces on lines 18 to 21, to be eventually filled in with the name of the purchaser, and the place and date. The second, fragmentary copy of the 31-line indulgence in the Scheide Library was issued in Erfurt, 22 October 1454, to Margaretha Kremer and her son Johann. Since Erfurt lies several hundred kilometers east of Mainz, the indulgence form itself must have been printed at least several days before that. The titling of the 31-line indulgence is set with the DK type; the text type appears only in this indulgence; there are also three initial letters, which appear to be cast in metal. The term limit of the indulgence was the last day of April, 1455, and a considerable number of the surviving copies were issued during the last days of the campaign. The Scheide Library's complete copy was issued on 29 April 1455 in Pfullendorf (Baden-Württemberg, 25 km north of Lake Constance) to Johannes Grosshans of Schaffhausen. It was preserved as pastedowns in a binding on four incunables of the early 1470s in the library of the Cistercians of Salem, which after the dissolution of that convent in the early nineteenth century was sold to Heidelberg University. The university removed and sold the indulgence as a duplicate around 1930. A surprisingly large number of copies -- 46 -- survive of the 31-line Indulgence, including many preserved as binding waste. Almost all copies were sold within the extensive archdiocese of Mainz. Several months later, a 30-line edition of the same indulgence was printed in Mainz. Its titling type is that of the Gutenberg Bible; its text type is unique to this edition; its three initials are different from those of the 31-line Indulgence. Only nine copies (including two lost in World War II) survive, none in America; most were issued within the archdiocese of Cologne, the earliest recorded date of issue being 27 February 1455. All copies of both editions were printed on vellum" (https://catalog.princeton.edu/catalog/4606221#view). 

Janet Ing, "The Mainz Indulgences of 1454/5: A Review of Recent Scholarship," British Library Journal, 9, 14-31.