A one or two day soak in ordinary white vinegar will turn up enough of a date on that, that is to say, if you’re curious. If not, don’t waste the white vinegar.
Yes, that's what you want to do with virtually every one of them. It'll wash them out some, but that's it. The vast majority of the time, it's going to bring up a date, and, if there, a mint mark. For a $2 gallon of white vinegar, you can't beat it, you're good for years...
