First, the raw numbers:
That isn't reassuring at first glance, but the ZVDB looks like it contains a lot of duplicates. Let's dig into the numbers a bit more.
|1496||Cicero, Paradoxa stoicorum (dedication)||1||1||1|
|1496||Tractatus de scorra||28||6||7|
|1524||Endlicher Beschluss 1524||0||0||1|
|1721||Friedrich und Maximilian||1||1||1|
There are actually only a few cases where ZVDD and DDB differ. The ZVDD knows about a 1787 edition of the Tractatus de scorra that the DDB doesn't list, and the ZVDD also includes a short work attributed to Grünpeck in one of Egenolff's prophetic compilations that the DDB doesn't include. That's not a huge improvement, however, as there are several additional facsimiles of other Egenolff editions beyond the ones known to ZVDD and DDB. On the other hand, the ZVDD has 4 redundant records for one edition of Grünpeck's Speculum, and 21 redundant records for various editions of the Tractatus de scorra, so that's one advantage that the DDB has. Finally, there are two missing facsimiles, one of the Prognosticum of 1532, and another of Grünpeck's Endlicher Beschluss concerning the conjunctions of 1524. For those, you'll need to refer to the Hungarian Electronic Library.