If it's any clue, the RPM kit brings not only a different set of wheels, but also a different axle for the gun carriage. In that respect, the guns preserved today have mostly the ealier type of axle, even with incomplete or modified brake mechanisms. Remember that the earlier type of brake was mechanical friction type, which must have been quite hard to control on the road. Most probably the brakes of the newer yypes must have been equipped by some sort of hydraulic mechanism.
I've read on several French forums that only 48 of these were completed for the French Army, half it seems completed during the war( two orders of 24) so I think its quite possible the German Army fielded more of the survivors and for longer then did the French... This may account for the fairly large quantity of photos in German service... Unfortunately I've not found anything to back this up yet....
I've seen a suggestion that the GPF was retained in production during the German occupation. There was another variant with 4 pneumatic tires which seems
to have been a conversion of the older GPF guns for the Wehrmacht.