Breeders and seed mongers are notoriously casual about seed storage. Most of the canna shows I go to, the seed sellers are keeping their inventory unsealed and unprotected other than the retail packaging. Marc Emery reportedly kept his stock in 35mm film cannisters in a drawer in his shop. I presume it's because they are turning over their inventory so quickly it doesn't matter.
My experience, having kept viable seeds for up to 20 years, is that consistent storage temperature and humidity are the critical variables to long-term viability. (So may be darkness, but I've always stored seed in the dark.)
Stored at room temperature in dry and dark conditions (baggie in a drawer in a house), 90% viability for 1-3 years; stored with desiccant in a sealed container in the fridge, 8-10+ years; frozen in sealed container with desiccant, 18-20+ years.
I've heard of many folks getting good long-term results >15 years with refrigerated seeds, but I've never gone beyond 10 years. With frozen seeds, one must be careful about thawing and refreezing when sorting inventory. I keep a spreadsheet of my seed stock so that I know what I am looking for before opening the icebox. I also give any beans moving from deep freeze to germination a day in the fridge to thaw and wake up before going into dirt.