A 'D' means that the Delivery note has been printed, but the order/credit note not delivered. It is possible to reset the Delivery print status using the blue arrow button.
A 'P' means that the order/credit note has been Partially processed, this could be that at least a quantity of 1 is delivered or invoiced all the way through to a quantity of 1 remains to be delivered or invoiced.
The order/credit note can be fully processed via the Detail window where the outstanding values and amounts can be viewed and the relevant action taken.
Once an order/credit note has been delivered, the detail lines cannot be amended nor can the whole transaction be deleted from the batch. If you try and delete it you will get a message saying the transactionhas been used and cannot be deleted. You will need to process the transaction through to the ledger and then post a reversing transaction.