Nothing that simple I'm afraid
.
The 19/14P was an export version of the Skoda vz 19/14 with modifications made at Polish request. An initial batch was purchased and production continued under license in Poland. Poland also had a stock of Skoda vz 1914 howitzers which were retrofitted to 19/14 standards (this mainly involved a new longer barrel I think) and these were redesignated wz 1914/19A. Of the whole 100mm stock only 4 were equipped with pneumatic wheels and served with the 10CB. There was no change of designation.
The wz 13 and wz 29 although both designed by Schneider and in the same class (105mm 'long range' gun) were different weapons. One (can't remember which) was fitted with a pneumatic-wheeled dolly for trials when the Polish Army flirted with the concept of motorising the divisional heavy artillery in the early thirties. The international economic debacle put paid to that idea and to my knowledge this was the only 105mm gun motorised in Poland.
Re the 120s the difference relates to the origin of the carriage 1878/09/31 used the Russian M1909 howitzer carriage while the 1878/10/312 the M1910. Twelve were converted to motorised traction without change of designation.
YC - I have a colleague who specialises in Polish interwar military export he may be able to give better informed opinion. Given that Poland was in dire shortage of ammunition for its own use due to problems with sourcing adequate supply of high-quality HE, I think your second option more likely (and when did Germany stop supply to China?). However this is mere speculation. One way or another I am sure many of my Polish colleagues would be fascinated by your 'made in Poland' shells so please let us see them if possible
