Of course, you can also do the same thing. They should keep proportionately longer if stored at cooler temperatures. This is presupposing they are kept very cool or frozen. Alfalfa is a unique seed as it actually germinates better if the seed is 2 or 3 years old. Most any sample of alfalfa contains 'hard' seed and 'soft' seed.
Soft seed germinates within two days while hard seed germinates in about a week.
The problem is, by the time the soft seed sprouts are ready to harvest, the hard seed may not have germinated yet. As storage time draws on, the hard seed turns into soft seed. Older seed germinates closer together. Stored in good conditions, alfalfa seed should have a good percentage of germination up until it is 8 years old. Total Vegetable Protein, made from soy beans, has an unusually long storage life.