So etimes if you look really carefully on the product, you'll see a clock type thing (sometimes more)
They show.... Year, month, usually just year.
Not all moulded plastic have it, but lots do.
So etimes it inside,so won't notice, and as I said, sometimes you get the month too.
Have a look at some molded stuff n look for the small clock looking dial... You'll need good eyesight tho!