Well basically Sd Kfz 251/17 we have is officially Sd.Kfz. 251/17 ausf. C mit 2cm that was specifically made for Luftwaffe as armored anti-aircraft vehicle that could keep up with mechanized units with some protection.
The controversial thing is that none of these saw service in Normandy or in France at all. Very few were made and only division that propably saw most use of it was the Fallschirm-Panzer Division in Italy.
However the Sd Kfz 251/17 that saw more service was based on the ausf. D version and its setup was more like this:

...Which production did not start until November 1944 (around the same times Sd Kfz 251/21 actually).
So why we have so many divisions with Sd Kfz 251/17 (and Sd Kfz 251/21) as there could not have been?
The controversial thing is that none of these saw service in Normandy or in France at all. Very few were made and only division that propably saw most use of it was the Fallschirm-Panzer Division in Italy.
However the Sd Kfz 251/17 that saw more service was based on the ausf. D version and its setup was more like this:

...Which production did not start until November 1944 (around the same times Sd Kfz 251/21 actually).
So why we have so many divisions with Sd Kfz 251/17 (and Sd Kfz 251/21) as there could not have been?