Spice vendors would like you to believe you need to replace all your herbs and spices once a year, if not more frequently. I don't do that, and neither do any of the professional chefs I know. (There is a noticeable difference between fresh herbs and dried ones, but once they're dried, the rate of change seems to be quite slow to me.)
I do think the type of container and where it is stored affects potency, though. In particular, the 'flip open' jars seem to dry out faster than the screw lid ones. And if you store them at the back of the stove or in a cabinet that is close to a heat source, then I'm sure they probably do dry out faster.
I do think that Penzy's may do a better job of pulling out-of-date items from their shelves than your typical grocery store does, but that assume you can find freshness dates on them at all. (Not every herb or spice has them, though most have tracking codes.)
And if you buy herbs and spices that are stored in bulk and weighted out when you buy them, who knows how long they've been there?!