Not a Sonor expert;
But my D454's have the same shell, strainer and extra hole below it.
Regarding to the plating process:
If I remember correctly I observed 1 maybe 2 1mm holes near / in the bearing edge. I reckon this might be the "plating holes".
Cleaning up will be a pleasure; you don't need much to clean this chrome of high standards ;-). Have fun!
This snare