Leica serial numbers are assigned in batches, not in a strict sequential order, so there is a lot of scope for lists to get things wrong. Any list is a 'more or less' guide, an estimate of when the bulk of the lenses in the batch was released by the factory. But some serial numbers may have been built well before, and some long after the dates on the list. The batch system is used by manufacturers where a lot of testing and adjustment is done, so sending a lens back to a previous station makes no difference to the serial number sequence because there is no strict sequence.