Answer
Express the whole traversal as a single SQL join chain instead of layering several separate custom-field-based lookup steps together: starting from Shipment Line, join to the internal Customer Order via its source reference, then join through the Customer Order Purchase Order link table, which connects an internal purchase order back to its originating Inter-Company sales order, to reach the external/originating Customer Order, and pull the coordinator/authorize code directly from that final joined record. A single multi-table join chain expressed this way is more maintainable and reliable than layering several separate custom fields, each independently looking up one intermediate step.