I haven’t gotten many flats (knock on wood) in recent times. Consequently I have tubes that are sitting unused either in my garage or bike bag for several years. At least two times within five years I’ve pulled out a tube from my bag to fix a flat and it would not hold air. I always pump a little air into a tube to test it before mounting, so I'm not puncturing it by accident during replacement. The brands have been different too. I store the tubes in a non climate controlled environment in FL. Is it possible they are dry rotting?