Here are some pics showing the differences in the VIS pistols:
September 1939 VIS:
This one was hastily put together during the Nazi invasion. The barrel does not match, but it is Polish marked - this is common among the "blitzkreig VIS". You can also see that it is missing the firing proof and inspection marks. The firing proof would go by the de-cocking lever, and the inspection proof would be on the triggerguard - in 1939 it would be a D over a 2 in an oval. I'm still to aquire a prewar VIS.
Nazi type I VIS:
This VIS is the early one made by the Nazi's. It was put together with remaining parts from the Radom factory, and has a cut for the shoulder stock. It also has a bunch of Polish manufacturing marks. The barrel is Waa623, so it was made in Steyr where the pistol was put together.
Nazi type II VIS:
This is the most common VIS varient. It has no cut for the shoulder stock, and is otherwise identical to the Type I. The finish is not as nice as the above VIS pistols.
Nazi type III VIS:
This is the last varient. Tooling marks promenant and the finish is poor. The takedown lever is omitted, and the decocker double as a takedown lever. This is why you will notice the slide noches are in different places. Grip eschutons deleted, that is the reason for the larger grip screws. The grips are brown to denote the difference.
Some argue that there is a 4th varient, that is purely made at Steyr after the Radom plant was moved there. It does not show FB Radom on the slide, and simply is stamped BNZ. It would also show a phosphated finish. These also have wooden grips. This is a varient I am yet to aquire.
Here are some pics of the shoulder stock: