Choosing a code
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What the code has to do
Indicate the day, month and year of manufacture. Any scheme that does that satisfies the wording; a scheme that indicates only a month or only a batch number does not.
The simplest honest scheme
The date itself. On a product with a year or two of shelf life there is often no reason to obscure when it was made, and a plain date needs no explanation to anybody.
Why anybody uses a code
A visible manufacture date on a product that sits on a shelf for a while can read as old even when it is well within life. A code avoids that without hiding anything from somebody who asks.
Keep the key somewhere permanent
A code nobody can resolve in two years is a code that fails the purpose. The scheme belongs in a document with the quality records, not in the head of whoever set the coder up.
Do not overload it
A code that encodes the date, the line, the shift and the formula version is attractive and fragile. The requirement is about the date; anything else you want to track can be a second mark.
Make it legible on the substrate
Black ink on a dark label, or an inkjet code on a glossy curved surface, can be unreadable in practice. The rule says clearly display, which is a judgment about the finished unit.
Check it on the line, not on the sample
A code that prints beautifully on a flat test piece can smear on a round bottle moving at speed. Pull units from a live run and read them.
Use the same scheme across the range
One format for every product makes the code readable by anybody who has seen one, including a stockist checking rotation.