Scent and shelf life
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Fragrance oxidises
Top notes go first, which changes the character of the scent rather than simply weakening it. A product can be perfectly safe and no longer the product the customer bought.
Light drives it
Which is the argument for amber glass and against a clear bottle on a sunny windowsill, where this product is very often kept.
Heat drives it too
The car leaf is the extreme case, but a bathroom shelf above a radiator is not gentle either. Storage conditions in this category are genuinely poor compared with most products.
Which makes the date code useful to you
The regulation requires it and you want it. When somebody reports that a bottle smells wrong, knowing it was made eighteen months ago is the difference between a formulation investigation and a shelf-life answer.
Test the way it will be stored
Warm, in light, for months, in the production container with the production sprayer. Smell it against a control kept cool and dark.
Keep a cool, dark control from every batch
It is the only reference that tells you what the product smelled like when it left. Memory is not a control.
Consider stating a best-before
It is not required by the VOC rule, which asks only for a manufacture date. For a fragranced product it is useful information and it manages an expectation the category frequently disappoints.
Concentration is a shelf-life lever
A higher fragrance load holds its character longer because there is more of it to lose before the balance shifts. It also costs more and pushes against the VOC budget, which is the trade.
Rotate stock and say so to retailers
A scented product that sits for two years in a shop is a different product by the time it sells. Telling a stockist to rotate is more useful than hoping, and the date code is what makes rotation possible.