Depends on what the meaning of "is" is. ;-)

What do you mean by "last?" It changes in nature when insects or microbes get into it, but it is still usable. Icky but usable. I try to use all my stores of organic ferts by Thanksgiving so I don't have to store them over the winter. I supposed if we ever had freezing weather, then leaving it in the frozen garage would be fine. All it takes is one good freeze to kill the insects.