[A] The production order is being created in response to a document like an OC or an SC. Reference number means the number of this Order Confirmation or Service Confirmation.
[B] This document number may be of a document like an Order Confirmation or a Service Confirmation
[C] If you are creating a production in order to create stock without any OC or SC, then you can add any reference number against which you are creating this production order or you can keep it blank
Keywords: Reference Number, Production Order