I have seen were 2 sets of pulleys were spot welded together from factory. usually a 4 grooves with 2 more added. and have had the spot weld drill to separate the 2.

they could be for balance but me thinks that would only be to N balance the pulley itself as I do not know of pulleys being engine specific only model/app specific. and E58 is a police engine correct? that could have needed more grooves for accessory's