In aerospace plants, no single MES KPI fully represents inventory accuracy. A practical approach is to track a small set of KPIs around stock record vs. physical count variance, lot/serial traceability integrity, WIP location accuracy, and backflush or issue errors, and then correlate them with cycle count and discrepancy data from ERP, QMS, and MRP. The value of each KPI depends heavily on data discipline, system integration, and validated processes.