[Product question] The FDA requires all sunscreens be good for at least 3 years, so why do some sunscreens have earlier expiration dates?

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I got a neutrogena sunscreen this summer, which has an expiration date this month. How is this possible? Has it just been sitting in the store in the back for 3 years? I doubt that, everything goes by so fast. Why do some other sunscreens also have a 6 month expiration date then? Does it mean I should ignore them and use them for 3 years? Sunscreens must comply with the FDA, right? Edit: the date it was made isn't indicated
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Submitted by Diligent_Soup2080