For experience: A year in jars is fine as long as you don't let it get too dry. However, it will lose some taste and potency and this seems to accelerate after around 6-8 months of curing. Vacuum sealed using a descent sealer (I use a Food Saver) and then placed in a second container in the back of a freezer will last for 2-3 years or more. You need to protect it from air, humidity, and temperature changes (from freezer door opening/closing).
I recently found an oz in my freezer that was from 2009. It was cured for a year (meaning I had better things to smoke) and then I vacuum sealed it in a Food Saver bag, tossed that into a plastic container in the freezer, and forgot about it. Taken from the freezer, the four year old buds were brown and dry, but not bone dry or crumbly. There was no smell or taste in the buds, but they were still potent when smoked. I made some really good QWISO hash with it. The hash is VERY potent and has a nice fruity taste.