A finished item that is serial number controlled is produced including a raw material that is batch controlled. For example BOM serial S01 contains COMPONENT batch B01. This BOM is sold.
Later, a Service order is created for BOM serial S01 and the Component B01 is replaced with batch number B02.
At this point there is no way to trace that now BOM serial S01 contains Component B02 and not B01, all tracing shows as it has B01.