What we found, and what it turned out to be.
A manufacturer: "MRP isn't planning our sub-assemblies"
Sales orders created the top-level production order and demand never reached the components under it. MRP was not broken. The sub-components were in the wrong item class. In the same engagement, scanning had never worked because the barcode field had never been populated, and a three-level approval map was quietly bypassing the route finance thought it followed. The first phase had one finish line: one clean sales order to invoice with full BOM-linked cost and GL sign-off. It was met on the target date.
A distributor: one document, three symptoms
Three months after go-live, one customer's items read unavailable, one invoice was short and the next would not create. One duplicate order keyed during cutover week had been reserving stock ever since. We cancelled it, cleared the orphaned allocations the recalculation could not repair, and the recovery shipment matched to the case.
A distributor: EDI orders with the wrong items
The EDI vendor said it passes through whatever the customer sends. The first theory was a reversed mapping. The actual cause was cross-reference rows written before the customer changed a pack size. Rows repointed, verified on live orders. During a separate outage, more than 150 staged records were reconciled to the order book before anyone deleted anything. None were lost.