Was the stuff you were having problems with factory ammo?? What brand?? While milsup ammo is sealed at the primer and bullet, considering how long some of that stuff has been around and still goes bang, I would think that modern ammo stored in any reasonable location would be good for several years.
The other day I shot up some homemade .300WM ammo that was loaded in '99. And it was sitting out in a unheated shop (temp swing 100+ in the summer and single diget in the winter) the whole time.
Help us out here.