Only way to know is if you sterilize them yourself.
As I've told you before, some UG-labs in some countries don't sterilize vials at all. I know this for a fact. I don't know much about how UG-labs run their businesses nowadays though.
When you get vials they are clean and packed so nothing will get in to them. They aren't sterile though.
When the vials are sterilized and sealed they aren't sterile forever. There are some rules/regulations of how long after they been sterilized they are considered sterile (talking about empty vials now). These regulations are probably just to stay on the safe side.
I've also mentioned this before but I'm doing it again. Rinsing your equipment, vials, rubber stoppers with alcohol only disinfectants them, alcohol doesn't sterilize them. This means that you have to sterilize you rubber-stoppers as well, not just give them an alcohol bath.
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