When Lot Tracking Is Not Enough: Designing WMS Serial Number and UDI Management

Why Track Individual Serial Numbers?

Most WMS platforms manage inventory by lot. Products made on the same line on the same day are treated as one batch, with a receipt date, expiry date, and quantity. That works well for food and consumables. But for some products, lots leave key questions unanswered.

Medical device UDI: Products must carry a standard identifier, and supply records must be reported

Electronics service and warranty: Warranty periods start from the date a specific unit was shipped or sold

High-value equipment and parts: Theft, rental, and repair history must be followed unit by unit

The difference becomes obvious during a recall. If only 120 units out of a 5,000-unit lot contain a defective component, lot tracking forces you to treat all 5,000 as suspect. With serial tracking, you can answer "which unit went to which customer" immediately and isolate the 120 affected shipments. That saves recall costs and protects customer trust.

When Should You Capture the Serial Number?

Full Scan at Receiving vs. Scan at Shipping

The first decision is where a serial number enters the system.

Full scan at receiving: You know the location of every serial while it sits in the warehouse, giving the highest accuracy. The cost is a much heavier receiving workload

Scan at shipping: Receiving is done by quantity, and serials are recorded only during outbound checks. It is lighter, but you cannot see which serials are on hand

Regulated and high-value items usually justify receiving scans, while consumer electronics tracked mainly for warranty often use outbound capture.

Parent-Child Aggregation for Cases and Pallets

Aggregation solves much of the workload problem. Suppose a pallet holds 40 cases of 10 units each. Scanning 400 units at 2 seconds apiece takes about 13 minutes. If the supplier sends case-to-unit relationships (for example in an ASN), scanning 40 case labels registers all 400 serials in about 80 seconds. The catch: once a case is opened and units ship individually, the relationship breaks, so disaggregation on case opening must be built into the process.

Barcode, 2D Code, or RFID?

1D barcodes: Cheap and universal, but limited data capacity

2D codes (such as GS1 DataMatrix): Hold item ID, serial, and expiry in a small space, which is why they are common for medical device UDI

RFID: Reads a whole case without opening it, but adds tag costs and requires a way to detect missed reads

WMS Data Model and Process

Per-Item Settings and Status History

Not every SKU needs serial control. The item master should define whether serials are tracked and when they are captured (inbound or outbound). Each serial then carries a status such as `received → stored → allocated → shipped → returned → scrapped`, with a full change history.

Validating Serials at Picking and Packing

When a customer orders a specific serial, the system must confirm that the scanned number matches the allocated one. Even without a designated serial, outbound checks should reject already-shipped serials, serials belonging to another item, and serials on hold.

Returns and Exchanges

A returned serial should be linked to its original shipment and received into an `awaiting inspection` status. Inspection then moves it to sellable, repair, or scrap. Recording the link to any replacement unit keeps the service history intact.

What to Check for UDI and Regulatory Compliance

Linking supply reports to shipping data: In Korea, medical devices must carry a standard code and supply records must be reported, and that data ultimately comes from WMS shipment records. If serial, customer, and ship date are captured consistently, reporting does not become a manual exercise

Standard formats vs. customer formats: GS1 separates the item identifier (01), lot (10), expiry (17), and serial (21), but hospitals and distributors sometimes require their own formats, so you need conversion rules

Confirm current requirements: Covered device classes, reporting cycles, and data fields can change, so always verify the latest notices and guidance from the Ministry of Food and Drug Safety

Common Failure Patterns

Missed scans: The quantity says 100 units but only 97 serials are recorded, and the gap grows over time. Block confirmation whenever the count and the serial list disagree

No rules for duplicate or unknown serials: When operators improvise, the data gets polluted. Define hold procedures and approval steps in advance

Disconnected numbering across systems: If ERP, WMS, and service systems use different serial formats, traceability breaks exactly when a recall needs it

A Phased Rollout

Rather than turning on serial control for every SKU at once, start with high-value and regulated items. Stabilize outbound scanning and history lookup in phase one, extend to inbound aggregation and returns in phase two, and complete ERP, service-system, and regulatory reporting integration in phase three. This order keeps risk manageable.

POLYGLOTSOFT designs serial number and UDI management drawing on our experience building WMS platforms and integrating them with existing ERP and service systems. From choosing the right capture points for each product to scan validation and supply-record integration, we support you step by step. If you need unit-level traceability, we would be glad to talk.