Vorpanzer F1, with extra bolted appliqué armour on the sides, gun mantlet and frontal glacis, with the 5th Panzerdivision, Group Center, Russia, winter 1941-1942.
The most complete story of the Vorpanzer for the PzIV Ausf.F is in the Band 5 (Neu), Begleitwagen, Panzer IV by W.Spielberger.
Here's a summary:
Conference 7.7.41- The Führer has been informed that in the battles in North Africa that armour-piercing rounds are becoming a problem from English tanks. The Führer asks that new production Panzer be equipped w/ spaced armour in front of the main armour.
Conference 29.11.41- the Fuhrer intends for all unit to be equipped with the new Vorpanzer.
Report from Krupp-Essen, 24.12.41- There is a shortage of material for the Vorpanzer... Due to the situation delivery of the first Vorpanzer is expected on Feb 1, 1942. There is a question, should the turrets be delivered w/ the Vorpanzer or not, that hasn't been made very clear.
There is more text but is doesn't mention about shipping of the Vorpanzer to combat units. The idea was dropped with the production of the Ausf.G with the longer 7.5-cm KwK. There is a photo of 2 PzIV with Vorpanzer, and the first has the name "Hansi" painted on it. There is no other markings to distinguish which unit it is. But by the overall look of the rest of the vehicles it looks like that it is a PzAusbAbt.