The problem as I see it. Is that, when you create a sales order the customer due date is being stored in BKARINVL.BKAR_INVL_ASD which allows you to track the real customer due date.  
 
The problem occurs when you invoice and post.  It creates BKARHINV and BKARHIVL records. The BKARHINV has the invoice date, order date, ship date, but the BKARHIVL.BKAR_INVL_ASD now contains the actual shipdate.  You now have lost the original customer due date and can not tell if you met the customers date or not.  
 
If you have not purged closed sales orders you still have the customer due date in BKARINVL.BKAR_INVL_ASD, but you can not relate it to the HIVL because you have no invoice number in INVL.
 
If you have purged closed sales orders, you have lost the customers required date completely.
 
In my mind the BKARHIVL.BKAR_INVL_ASD should retain the original customer due date because the actual ship date is recorded and stored in BKARHINV which is linked to BKARHIVL.

I'll give it a look.  Thanks,

You are right, it is ISARHCHG and you need to run UT-J and rebuild the DDF to get to it in Maintain DB.