How to enter a SN into an IB whose part number was recently changed to be serialized?
I asked a similar question a few years ago, but it resolved itself before I got to the bottom of the problem.
A given part number is currently set up to be serialized at sales order issue. An IB record for that part, created several months ago, has a value in csi_item_instances.mfg_serial_number_flag of 'N', indicating that at the time of the IB's creation, the item was NOT serialized. The last_update_date of the part number setup in mtl_system_items_b is 23-JUL-20, so this item was apparently recently changed to be serialized.