I don't know if they work "perfectly well" but i have 2 varieties of cilantro seed from at least a year ago and they germinated and are growing for me.

Each year, I let my cilantro seeds dry out completely on the plant, then I shake some over the ground and collect others in a zip lock bag. (Just in case I want more, or I want to start another plant for someone, etc.,) I haven't bought Basil or Cilantro seeds in years.
Mary

I have seeds of all kinds that are ranging from a year to more than 10 years old or more. The longer they are sitting around, the less they will germinate. For coriander seeds, a single year of time will yield about 95%, for 2 years, about 75%, and 4 years, about 40 to 50%. After that its a toss up. Because I use coriander to make sausages with, the seeds are used in that instead. The ones I use for the herb (cilantro)are the slow bolting type and are a bit longer lasting for the leaves. Coriander is the seed name, while cilantro is the herb leaf for that plant.

I heard they found 2,0000 year old seeds in the pyramids and some were still good. I keep my unused seeds in the refrigerator for storage for up to two years. I'd say I get 90% germination of two year old seeds. Just keep them dry. Dampness will make them grow in the fridge.

OOps, I meant two thousand year old seeds, not twenty thousand.

Just like mummys, the seeds that were found were protected against many environmental changes. The desert is one place where things can last for many centuries.