"Use by" is dumb, it's too close to "Best if Used By." If there's a safety issue, the term should be "expires", "expires on", or something like that.
For salt, that seems somewhat silly, but not enough to make me fundamentally distrust the rationale
It does seem to go “flat” after a few months regardless, even when the expiry date is 2 years in the future.
Then they switched to 30 days recommendation to goose sales.
A sell by date makes perfect sense on salt. No packager wants to be responsible for material that sat on someone else's shelf for years and years.
Luckily the packaging had started to biodegrade, too, so it was easy enough to scrape off the fiber fuzz and hammer down the inner salt rocks into something useful. Better than nothing! But I wish I’d been able to buy it by its sell-by.
(Spoken as a skeptic of deadlines of all sorts, and one who routinely ignores food safety. I still think the dates are mostly silly, but that type of instance reminds me why it’s a hard problem: even if you’re not a dastardly wastemonger, choosing the “right” date depends heavily on handling and climate and factors beyond your control—unknowable at production time.)
My broader point, I guess, is that the appropriate date to sell something by depends so heavily on factors unknowable at production time that it’s hard to guess. But also that apparently-shelf-stable goods can in fact degrade.
And I guess that it’s kind of weird and unnatural the way modern industrial packaging/processing have trained us to expect that a given product should be interchangeable with any other until an arbitrary date.
I am a human capable of parsing natural language semantics, and "use by" is terrible. It's one of those completely unexplained commands you often find in instructions. Why should I use it by that date? If you're not a mindless drone who just unquestioningly follows instructions, the total lack of reason creates a lot of space to decide to do something else. For instance: without consulting California food labeling legislation (which, I admit, Californians all carry around the statute book those regulations several times a day), it's reasonable to interpret "use by" as "best if used by," for instance.
They should use clearer language because they can and have no excuse not to.
The compromise here is to keep printing as short as possible. I think the greater issue is that these statements don't point to any trivially available authoritative definition.
They have no excuse.