Depends on the manufacturer. A lot of preferred powders are imported by Hodgdon from Australia. Those are only shipped in once or twice a year, and then re-packaged from bulk containers into 1-, 4-, and 8-pounders for retail. The dates on your retail containers may not be the actual powder manufacture dates.
West coast ports were all backed-up during China flu with ships waiting for dock space and to be unloaded. Lots of different goods (to include those Ozzie-made powders) sat in ships for a while before heading to wherever Hodgdon re-packages (I think Kansas).