Great tip about checking by eye (and nose) rather than just the sell-by date. Likewise, some (usually ones I harvest myself) last longer than a shop may say. Yarrow is one of those, when the stems are quite strong and thick, the result is a long-lasting dried herb. I sadly lost a lovely glass jar of self-harvested Calendul flowers last week. It was from a year ago, was great, fresh and well-scented, then suddenly it became fishy and I had to compost it. Sometimes, even in glass jars, when opened some damp air gets in, or something, and spoils it. Great compost ingredient anyway!
Foraging, Growing and Using Herbs in Cities