I think this particular process in DBA has always been kind of cumbersome.  Ideally, I would like to see a flag to indicate what state a given sales order is in.
 
For example:
    1. Order entered and waiting to be released to shipping (RTI='N' ? )
    2. Order Released to shipping, but not shipped yet (RTI='R' ?)
    3. Order Shipped but not invoiced yet (RTI='Y' ?)
 
This would allow better batch processing of Packing Lists and Invoices.
 
One could print packing lists for all Released Orders within a Sales order or Ship date range.  This could flag them as released to shipping.
 
When Shipping responds with which orders were shipped and any changes, shipping charges can be plugged into each order, and they could be flagged for invoicing.  
 
When Invoices are printed, It would only print invoices for orders that have been Flagged.
 
It seems like there has always been a missing state because of the Simple RTI 'Y' or 'N' flag.  Because of this, it is very difficult to release additional orders because you can't tell what is available to ship until Invoicing and posting occurs.
 
We only ship between 10 and 40 orders per day and it is cumbersome to process, I can't imagine what trouble it is for those that ship >100 orders per day.