Production dates only started with 40+ balls
Currently rubbers don't have them
I guess you would need an honest shop to answer you the age of the stock.
From my side, I try to order 4 times (per supplier) a year than oppose to 1 or 2 shipment.
It will cost me more, but I rather have fresher stock.
As my shop isn't really my income source, as it is more for promoting the stop and assisting with development, at times I would run huge specials just to clean my "aging" stock.
back to rubbers,
some are sealed, some have air holes in the packaging (so the rubbers was aired before getting to me)
just for some interesting fact, I had KTL stranger OX rubbers that somehow melted onto the hardpaper cover.
The Stranger is a very sticky rubber (had to peel off the hard paper), but the stock when about 1 year becomes a total write off as no matter how I peel it, the rubber is stuck on and with a bit of force, the rubber tears.