The "VD16" I mentioned in my previous post is the Verzeichnis der im deutschen Sprachbereich erschienenen Drucke des 16. Jahrhunderts. It's a constantly updated index of all known editions printed in German or in the German-language area in the 16th century. The interface is awkward and the project is woefully underfunded, but VD16 is incredibly valuable for studying 16th-century printing and early modern literature. Recently, the VD17 index became accessible through the same interface, so you can search two centuries at the same time. To learn more about it, read here, but to search the database, click here.
One thing I wish more scholars would do when citing German 16th-century editions is to include the VD16 number. As printers could and did print several editions of the same work in the same year, identifying an edition as "Augsburg: Heinrich Steiner, 1530" is not specific enough (let alone "Augsburg, 1530" or simply "1530"). With a VD16 number, readers can look up precisely what edition is meant, and find the cataloging source, and possible links to digital editions, and (via the "SFX" module) the shelf marks of known copies.
When I was researching Printing and Prophecy, I identified likely title words and checked every year from 1501-1550, and later checked all the authors for works I may have missed, and then double-checked every entry in the appendix against VD16 before submitting the final manuscript. For any research project that even tangentially deals with 16th-century German printing, VD16 is absolutely essential.