I think that at that time there was a lot of experimenting, and creating new cartridges was easy.
Probably less "red tape" than a wildcatter in Germany will face today...

Cartridges for a new caliber were probably loaded inhouse, as was done already in black powder times, creating additional income for the gunsmith, and ensuring quality control and customer binding.
Compare Scheiring in Ferlach, who provides hand-loaded ammunition for his rifles even today.

And if the gunsmith could sell a few more rifles by listing another caliber, that was fine.