When does the master inventory list (MIL) remain valid?

The master inventory list (MIL) remains valid until the contents change because it is designed to reflect the current status of equipment and items. Any modifications, such as the addition or removal of items, will necessitate an update to ensure accuracy. This ensures that the MIL provides a reliable reference for inventory management and accountability. Maintaining an accurate inventory is crucial for aircrew operations, as it directly relates to safety and mission effectiveness. In contrast, other options would imply that the list could be considered valid based on time intervals or conditions that don't align with the real-time nature of equipment management. Therefore, the focus on changing contents captures the evolving nature of inventory and the need for continuous updates to the master inventory list as items are introduced or removed.