Bill-backs are how off-invoice pricing is settled. The buyer pays standard cost up front, sells at the authorized price, and then claims the difference — which means the margin on the sale is not realized until the claim is paid.
Two failure modes dominate. Claims that are never raised, usually because the link to the authorization was lost or because volume peaked when administrative capacity was lowest. And claims that are rejected and never reworked, because rejections arrive as a per-line file that somebody has to interpret rather than as a worklist with the original transaction attached.
In foodservice distribution, where deviated cost is the core margin model, bill-back recovery rate is effectively a gross-margin metric: every unrecovered point is a sale made deliberately at a loss.