Every container, every unit
On this page9
The requirement
"The container or package of each consumer product that is subject to this subpart shall clearly display the day, month, and year on which the product was manufactured, or a code indicating such date."
Read "each"
Each container. Not each batch, not each case, not a record you keep. Every unit that reaches a customer carries a date or a code for one.
A code is allowed
Which is how most of the industry does it: a short alphanumeric that resolves to a date. That keeps the front of the package clean and still satisfies the rule.
Free samples are excluded
Products distributed to consumers at no charge for sampling purposes are outside the labeling requirement. That is a narrow exclusion about free goods, not about small sizes.
It is a production decision
Something has to apply a variable mark at fill: an inkjet coder, a hand stamp, a printed lot sticker, or a label with a cleared panel written on at packing. All four work and all four have to be chosen before the first run.
The artwork cannot carry it
A date printed in the label artwork is the same on every unit, which is the one thing the requirement rules out. Leaving a clear space in the artwork for a variable mark is the usual answer.
Which means a label layout decision
A panel that is clear of print, flat enough to take ink or a sticker, and positioned where a coder can reach it on the line. On a round bottle that is not automatic.
And it is useful to you anyway
A date code on the unit is how a complaint four months later becomes a traceable batch rather than a guess. The regulation is asking for something a careful producer would want.