As always, John M is exactly correct (well, almost always-and correct a lot more often than I am)!!!
It is interesting that in the 1904 DWM catalog, which was probably put together in 1903, shows an earlier bullet style than the truncated 278F bullet. This is a somewhat blunt RN bullet designated the 278C. This catalog is the ONLY reference source for this bullet. The ealiest 9mm cartridge for the Luger pistol is generally referred to today as the 9mm Borchardt. It had a very blunt RN bullet with a step at at the rear to allow for the case outside diameter at the casemouth to be 9mm thus allowing for a slight shoulder in the case. This bullet isn’t documented in any of the DWM documentation I have seen, but I suspect it was the 278A or perhaps 278B bullet. The 278C bullet illustrated in the 1903 catalog lacks the step in the bullet of the 9mm Borchardt, so the 278C was clearly intended for the current style 9x19mm case. Most, perhaps all, of the 9mm Borchardt cartridges originated with a gunsmith in Baltimore MD who gave them that name. The first trials of a 9mm Luger pistol were the US trials of 1903 -1904 (a 9mm Luger was offered to the British in 1902 but no testing was done). It seems probable to me that the 9mm Borchardt cartridges found in Baltimore came over with that trial. The first three trial guns 10029B/30B/31B which are all now chambered for the normal 9x19mm case. I suspect at least one of these pistols was chambered for 9mm Borchardt and had that barrel subsequently replaced with a 9x19mm barrel. If this is true, then the 278C bullet and/or the unknown 278D & 278E designs could have been part of the later US testing of the three test pistols. By April 1904, 50 9mm pistols and 25,000 rounds of 9mm ammunition were delivered to Springfield for testing. Regardless, sufficient 9mm Luger cartridges were loaded with the 278C bullet that this bullet was listed in the 1904 catalog, and the 278C bullet was designed, and probably produced, before the 278F truncated bullet.
I think it is pretty clear that the FIRST 9mm Luger cartridges had blunt RN bullets. The headstamp was probably DM * K * which is the headstamp on the earliest 9x19mms as John said. I suspect that some of these actually came to the US, but as far as I know, none have shown up either in the US or in Europe.
The famous truncated bullet which appears identical to the 278F was submitted to the German Army trials in March 1904 and the Navy trials in July 1904. The first pistols were not delivered to the Navy until 1906. It is likely that the 25,000 rounds of ammunition supplied for the US trials of the 50 pistols were also 278F loads.
I would highly recommend Geoff Sturgess’ excellent article in IAA Journal 444. It is an excellent description of the origin of the 9mm Luger cartridge.
Note that John gave you the facts, and I have followed up with the speculation.