A 9 mm Bergmann-Bayard with headstamp K DWM K 456B would be made in Germany, not Spain. It is a commercial headstamp, and some were sold in/to Spain, as a Spanish-language box label is known, designating the cartridges within as “DWM Cartuchos 9 m/m Bergmann para modelo reglamentario.” Similar 25-round boxes with the designation “No. 456b/247 Kal. 9 mm” are known from the Karlsruhe Factory. This headstamp is found with and without serifs on the letters. There is also one that has a trinomial headstamp of simply “D W M” with no case number, factory initials, or caliber designation at all.
This caliber was also made later at the Berlin-Borsigwalde factory of DWM, heastamped “B DWM B 456B.”
A nickel-plated dummy round was made with the headstamp “K DWM K 456A,” with letters having serifs. In our study of this caliber, we have found no ball round with this headstamp, although the DWM case register shows this number as the “Patronenhülse Kal. 9mm Bergmann (Bayard) Thieme & Edeler, Eibar.” However, it also shows case number 456A1 as simply “Exerzierpatrone Kal. 9mm.”
Finally, and said to be of DWM manufacture is the headstamp “STAR 456C” on an ordinary ball cartridge. The city of Eibar was the firearms manufacturing center of Spain. While some report that this cartridge was made for the firm of Bonifacio Echeverria, Eibar, likely because their brand for pistols was “STAR,” it is more likely that it was a contract for the Star Trust Corporation, a Basque firm also in Eibar. Whether or not the two companies had a business relationship is not known to me The DWM case type register shows this “456C” cartridge having a case cannelure; however, actual specimens do not have that feature.
The last DWM Catalog in our possession still list the 9 mm Bergmann-Bayard cartridge as available, under the description “Caliber 9, 456B Colt-Browning, Star, Bergmann-Bayard” and mentioned it could be supplied on strips (likely what we would call stripper clips, or chargers). It is presumed that these would be for the Bergmann-Bayard, and therefore would hold six rounds.
The original DWM number 456, sans letter-suffix, was likely the second headstamp, following “* D.M. * K.”, for the 9 mm Bergmann Mars cartridge, and for the early Bergmann-Mars pistol. However, it is found with over-all cartridge lengths of 1.330" - 1.339", and may represent a continuing development of the cartridge. Some K DWM K 456 cartridges, with no suffix letter on the headstamp, fall into the case measurements of a standard Bergmann-Bayard cartridge.
Reference: “The 9 x 23 mm Rimless Pistol Cartridges,” a Woodin Laboratory study compiled by John L. Moss and published by GIG Concepts Inc.