HI Michael,
The links between RDR1 & DLN1 should be using base line from target doc, RDR being sales order is the base of a delivery, but only if the delivery is drawn from the order - a delivery can also be drawn from a reserve invoice. You should also be checking that the base object type is the same (i.e. an order object type is 17 from memory, an invoice is 13 etc) to be sure that you are drawing the detail from the right base doc,
There is only a join between RDR1 and POR1 if the PO has been created from the sales Order - the target is not recorded on the sales order, but the base is recorded on the PO - again the BaseType, BaseRef and BaseLine need to be checked.
It is possible for one base doc to be drawn to multliple target docs too