Self explanatory really- you can see how Bachmann changed the frost grill on later locomotives. Rather than fix the errors along the center of the locomotive, the frost grill shape has been modified to make it fix the locomotive. Both the Bachman grills were scanned together and then the first run grill was resized in photoshop to match the grill in the prototype photo.

The first run is on the left- note how Bachmann has lowered the model in subsequent runs.

The only thing right about the bodyside was the first run frost grills...