You might see some crossed-out items on your packing slips. Those are out of stock items, which are confirmed the evening before your delivery. You might also see some Highlighted items or a "CR" written in front of items. These are often items that we expected to receive a shipment of the morning of your delivery and/or we felt the quality was subpar.
In both cases, we credit accounts within 24-48 hours. First, we go through the crossed-off items and then the highlighted ones. So you might see two different credits relating to one order (if you have both instances). You can view all account credits in My Account -> Payment History. The credits will automatically be applied to your next order.