I bought some green bean seeds a week ago, I just ripped open the bag, and there's no way to reseal it. Anyway, a week later I compared the beans I have with the ones still in the store. Mine were a little thinner and edgier (less round around the edges). The two bags are from the exact same supplier. I'm not sure if the shrinkage is from exposure to oxygen or something else.
What accounts for this (pretty small not very noticeable admittedly) change in the beans?