Consider a laboratory that orders one customized refrigeration cabinet for delivery in six weeks. The distributor does not stock it because it is expensive, bulky, and rarely ordered. A supplier can build it, another warehouse may occasionally hold a suitable unit, and an internal plant can make a related configuration. If planners treat all three possibilities as ordinary uncommitted supply, another order could consume the selected unit or capacity. Back-to-back fulfillment addresses that allocation risk by creating supply in response to scheduled demand and maintaining a firm link between the demand and its supply document.