Hi Cerjak.
Thanks for the additional photos. That helps a bunch.
To me, this gun with the short butt stock was made this way. The brass decoration and bone butt cap at the heel of the stock all look correct. If a rear portion of the butt stock were damaged, or otherwise missing, it would be little effort to simply add the new wood and re-install the bone butt cap. But I have seen photos and held many that were obviously made short this way.
I had the thought that the short butt stock might might allow the shooter to fire from the waist area while on horseback ala blunderbuss knee pistol style. Which I guess could be done. But then, there would be no need for a rear sight. And the pistol would be a much handier weapon on horseback. My only conclusion at present is that they were made for aiming/firing from the cheek, with the arms taking the recoil vs the shoulder. Just my best guess.
Although not as nice as Cerjak's, here is another example with the short butt stock.
Rick