As far as I know, date codes are not required or needed on rechargeable batteries. They are delivered in an uncharged state.
If you want to guarantee that you do not get junk, buy a genuine Canon battery from a reputable source, i.e. direct from Canon, Amazon (not Amazon Marketplace), Best Buy, etc. However, you will pay top dollar for a Canon battery; you could buy a used S50 with a (used) battery for the same money.
I have bought 3rd party batteries for other devices and have not had problems, but there is always risk going that route.
My Canon S50 camera, bought in 2003, could use a new Li-ion rechargeable battery, NB-2L, or NB-2LH high capacity. There is a vast difference in prices online, whether standard 570mAh or 1700mAh.
How can a person know which ones are junk and which are recently manufactured fresh quality batteries? I see no mfr. date on my existing ones, so how can I trust that what I buy now isn't knock-off junk and/or already several years old with little ability to hold a charge anymore?