They will stop looking edible before they stop being edible.

It probably won’t make you ill immediately, more likely the texture or flavor would begin to suffer first (hence “best by” rather than “expiration” date). Keeping it stored properly (i.e. not an open bag but something sealed) would likely allow it to last longer.

You should probably not eat 3.5lb of candy within 10 days unless you are trying to make your intestines suffer, but if you choose to binge please update us as to the state of your health so that you may be used as a cautionary tale.

“Best Before” is not an expiration date, it’s just so that if you aren’t satisfied with the quality after that date the company can say, hey we warned you, we can’t guarantee they’ll be up to our standards that long.

They aren’t going to suddenly go rancid on November 14

Since you already received the genuine answers:

You need to be really careful. The expiration date isn’t exact, but after that, they’ll quickly ferment and turn into Surströmming on the inside.

“best by” isn’t an expiration date, it’s just a product suggestion.
Only a very few things, like baby food, have an actual expiration date that’s meaningful.

Treat them like any other food. If it looks fine, smells fine, feels fine and tastes fine, it’s probably fine.
They’re basically entirely sugar, so the biggest worry is going to be drying out, not spoiling.

In the US, the “best by” date means nothing. They just want you to throw it away so you buy more. If it looks fine, smells fine, and tastes fine, it’s fine.

Probably for awhile, it’s a hard gummy candy. They’ll harden but I’m not even sure they can go bad.

Swede here. As a certified specialist in Swedish fish storage I recommend the following:

Divide the 3.5 pounds into smaller portions and store in separate containers (fx Ziploc bags).

That way they won’t go stale as fast since the unopened bags will retain the moisture.

Best before dates codes are more what you’d call guidelines than actual rules. Yar

This got me so confused, and I’m Swedish lol.

Quit well, I imagine.

worst case scenario, they get hard?

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You’ll be fine. That’s not an explicit expiration date. It’s just a date to be guaranteed a minimum quality.,

It would take an awful lot of time or other circumstances for swedish fish to become inedible. They’ll just get “stale” (with gummy candy, this is usually just getting a bit harder/chewier) and, in my experience with gummy Lifesavers, the flavor becomes more concentrated. I actually like that stuff just a little stale.

You should probably just eat them all. Right now. In bed.