Usually plastic, no matter if it's diet or normal sodas, are given a 3 month shelf life. Cans, for HFCS/sugar, it's usually 9 months. Anything with aspartame (Nutrasweet) in it, is 3 months regardless of the container. Not sure if there's a standard for sucralose, although Pepsi gives Pepsi One a 6 month lifespan. Glass, well glass has become uncommon enough that I don't know if there's any set standards anymore. Back when I used to buy Pepsi in NR and returnable glass, it was 9 months, but the product would actually stay OK for months after that, provided you didn't store in direct sunlight.
I remember posting an expiration date on some Frostie Root Beer that I found amazing once, looking back at that post, it was like 78 weeks from bottling til expiration! Never found out the reasoning why - maybe it's the amber-tinted glass it was in or something.
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http://www.bevnet.com/bevboard/bevbo...xpiration.html )
-Andy