Most schools using OPS do NOT accept back orders. It is written on their POs in the customized text at the bottom. Back orders are indefinite and can arrive after the semester is over. They also cause all sorts of issues with billing because the vendors often send you an invoice without the back ordered item, then send another with the item at a later date…thus creating 2 invoices/orders. We highly recommend that you set your school policy to not accept back orders. Often you can cancel the item and order it from another vendor.
If you must accept them, than the proper procedure is to leave the back ordered item at ‘processed’ while all orders are at ‘received’ and keep the order status at ‘partially received’ (or if billed advance the item to ‘invoiced matched’ while all others are at ‘paid’ and advance the order status to ‘partially paid’ if you must pay for it before the last item arrives). Either way prepare to get a head ache.