Leave it as it is. It will be fine. When the needle wheels are installed on the shaft, a jig is used to get it in exactly the correct position on the shaft. If its slightly too high on the shaft, it will hit the pump face when the motor powers up and potentially burn out the motor due to the friction and increased loads caused by the needle wheel hitting the face. This assuming it spins at all. If its too low, it will won't perform properly.
People sometimes get careless and drop or break their impellers. If they sold the needle wheels separately, chances are the warranty rates would be effected because people would install the wheels in the wrong position causing the scenarios above. Thus, Germany has decided against doing that. The good thing is that a couple missing pins will have no appreciable impact on the pumps performance.