I have an article coming out in an upcoming volume of Archiv für Geschichte des Buchwesens that expands on my discussion of practicas in Printing and Prophecy. One of the things I added to the discussion is a comparison of early German production to elsewhere in Europe. I put together a graph, but it wasn't as essential to the article as other graphs, so I cited the statistics in the text instead. Here's the graph:
Italian astrologers are usually credited with being the first to publish their annual prognostications, and with contributing half of all practicas before 1501. The first statement is probably correct; it looks like the Italians have a head start of around four years, and Italian production is clearly in the lead before 1480. But German production quickly catches up and moves into the lead by 1490. Based on what appears in the ISTC, German production for the fifteenth century comprises about 49% of the total, followed by Italian production at 44%. Despite some early production in the Low Countries, practica printing remains marginal everywhere else in Europe during the fifteenth century.
The usual caveats apply, though: I've examined the German sources much more closely than the Italian ones, so I'm undoubtedly missing a few Italian practicas, and one has to be extremely cautious when making statements about fifteenth-century production based on twenty-first century preservation of ephemeral booklets.