@Jaeger ... I am going to respectfully disagree with the info in that book - but ONLY because I don't like the use of the word "produced". When it comes to people (like me) who want to know when they entered combat, production doesn't mean anything. Being inspected, being signed-off as passing inspection, being shipped to and distributed to combat units, having them train with them so they are ready to see combat, and THEN entering combat is what matters.
The 251 Ausf A was in development for a few years (I have seen sources state either 1937 or 1938), but the first production models were delivered to military units in Spring 1939. Only one of the Panzer divisions that saw service in Poland were partially equipped with any of these (the 1st Pz Divisions). And they were NOT fully supplied. Many grenadiers from this unit still rode in trucks! Production ended in mid-1940.
The 251 Ausf B was a direct result of combat experiences in Poland. The design was simplified a bit to speed production. These were produced until late 1940.
The 251 Ausf C may have entered production in January 1940, but they were not delivered to military units until the summer of 1940 ... too late to have seen any combat in France or the Low Countries. So there were no Sd.Kfz. 251 Ausf Cs used in France 1940.
Which is why I would love to have a kit that allowed me to build either an A or a B ... because those are the only two models that saw any action up until the fall of France in 1940.
As for production numbers, the Ausf A and Ausf B were produced in limited numbers (maybe 500 of each). Total production of the A, B and C is 4,650 - so the majority of those first three models was the Ausf C,
Compare that to the Ausf D, which they built 10,602 of. And since it appears that most gamers prefer the mid to late war period, this is the model that would most likely be seen.
So I see why a model company would offer up the Ausf D, and if they really wanted to make gamers happy, the Ausf C. And I can see why the Ausf A and Ausf B might never see the light of day. But I can hope :-)