Many Small Improvements
The contract didn't mean that the B.W. I Kp would go into production without changes. Trials showed that many small improvements had to be made to the entire design. This is a perfectly normal situation; history knows few cases where a mass production tank did not differ from its prototype. However, the B.W. I Kp had no major differences from the production tank. The overall concept of the tank proved successful and did not require serious changes.
Despite a lack of major changed, 1.Serie/B.W. officially indexed Pz.Kpfw. IV Ausf. A, retained only 7 components that were completely unchanged. Among them were the radiator, engine compartment bulkhead, brakes, and transmission elements. Everything else had to be changed in one way or another by Krupp engineers.
It's worth focusing on the ammunition rack detonation closely. One of the PzIV's main problems was that its ammunition racks were located around the entire perimeter of the fighting compartment. It was difficult to avoid hitting the ammunition. Since most of the tank's shells were of the high explosive variety, the odds of detonation were high. Because of this, the PzIV is the uncontested leader in the gloomy parade of destroyed German tanks. Flying turrets, frequently detached from the hull along with the turret platform, were a common sight.