Sorry the theme didn't work for you. I'll stay away from things like this in the future so that we're all working from the same standards.
Well - maybe you could try to formulate such themes so that one can work by the idea instead of the exact definition in case the definition doesn't match? Basically I like that there are new ideas in this challenge, book properties other than pictures on the cover, words in the title or first letters of authors. I'm not complaining. With some stock of english books available and the fact that many people here occasionally read books in English so you can release english books without having to search much for a suitable place to put them, I'm ok with counting only english books this week.
Anyway... for those who might be interested a little bit more about german paperback sizes.
The largest, and also the oldest, of our large paperback publishers is Rowohlt, with the "rororo" series. Almost 8% of the books on my shelf (or about 13% of all paperbacks) have been identified as rororo editions. "rororo" was short for "Rowohlts Rotations-Romane", which means "Rowohlt's rotary novels" and points at the fact that they were basically the first to switch from quality book printing to cheap newspaper-type rotary printing for large print runs. So, their standard size was proably derived from some newspaper paper size and with 19 x 11.4 cm, it came out even slightly larger than the "oversize" mass market. They kept this size from the start in the 1950s until about 50 years later.
However, most other large publishers did not copy the rororo size. Through the 1960s to 1990s, most used 18 cm long books with different widths. From the number of books on my shelf, the books from #2 (dtv), #4 (Fischer) and #8 (Suhrkamp) came out at about 18 x 10.5 cm, while #3 (Goldmann), #5 (Heyne), #6 (Diogenes) and #7 (Knaur) are wider, near 18 cm x 11.5 cm or even up to 12.5 cm. No large publisher made shorter books than 18 cm for the mass market, so they all are kind of oversize by american standards.
During the past two decades, all larger publishers switched to larger book formats. Many recent editions are about 19 x 12.5 cm.
They also switched to "better" paper and often to larger print, which made the books significantly heavier. For example, the classical dtv edition of Heinrich Böll's "Die verlorene Ehre der Katharina Blum" was 85g of paper, while the new printings of the "same" edition come with about 175g of weight! During my almost ten years of bookcrossing, this made my average release bag significantly heavier, and it got subsequently more difficult to build up a stock of lightweight books in case I want to release more than a few ones outside. Since I almost never go by car but use my own feet, bike, public transport, or occasionally horses, to carry my books, weight is an issue after all.
However, the larger books are a matter of generations in Germany, not of editions. At the same time dtv introduced the 19 x 12 cm size, they stopped making the classical 18 x 10.8 cm editions. There never has been a common "premium" size like the US trade paperback. Some publishers introduced larger "premium paperback" series, but they never got popular.