A defect claim is not really a question about a product, it is a question about a production run: which components went into this unit, when was it built, what did the test data look like at the time. Factories that can answer that are diagnosing; factories that cannot are negotiating.
What a date code should identify
At minimum: the model, the production week, and the return. Practically, it should also point to the batch record — the component lots used, the incoming inspection result for those lots, the in-process checks on that run, and the outgoing report with its measured values. That is four documents behind one short code, and it is the difference between a same-day answer and a week of correspondence.
Why it matters commercially
A claim on one batch can be contained if the traceability exists. The factory checks whether the same component lot appears in other shipments, and if it does, the affected consignments are identified before the customer finds them. Without traceability, every shipment is suspect and the only safe response is a recall.
What buyers should require
Three things, stated in the purchase order. First, that the batch report travels with the shipping documents. Second, that the date code is printed on the unit or the carton rather than only in the factory’s system. Third, that the component lots used in a run are recorded and available on request — not in every shipment, but on request when something goes wrong.
The uncomfortable part
Traceability is only as good as the discipline around component substitution. If a purchasing decision to use a second-source capacitor is not recorded against the batch, the trace leads nowhere useful. That is why the record of substitutions matters more than the record of the parts that went according to plan.