Susan Ashford has a book, Seed to Seed, that is worth reading. She writes about all the main plamt food groups, how to propagate the seed, how it can or cannot be cross pollinated, and how to store it.
As I recall, most seed lasted for 4 years, if stored in cool, dry conditions.
BUT...onion seed is very fungible...may not last a year....except for chives, which last quite well.
AND...if you freeze seed....there is something you are supposed to do...like not take it out of the container, or thaw it in the refrigerator, because too quick a thaw can rupture the seed body.
I have grown 10 year old corn seed.
But this is why you should seed open pollinated seed: You will find that some plants adapt better to your mini-environment. Those seeds should be kept, but eventually you have to bring in new stuff, as Ashford says you need about 60 plants to maintain the gene pool...and I REFUSE grow 60 zucchini plants!