Stock availability for specific customers

Seeking inputs from all of you on how to get visibility into inventory availability by lot number, whereby specific customers have stringent requirements. We would prefer to avoid creating new item numbers just to identify stock for such customers. When sales checks inventory levels in the system, they need to know the available quantity that meet the customer's requirements. I am wondering how others manage this, if creating new item numbers is the only way? We also considered utilizing the lot number's category codes to manage this requirement. But we tested when a reclassification is done, the newly created record