I stored 500 9mm primed brass in an open coffee can, sitting on a shelf in the storage shed for over 13 years. No heat either. Worked it all up last month. Took it out to the range for some practice and not a single issue with it. Every single one fired like it was new.
I was worried because I had totally forgotten about it. BTW the powder and all the components were 13+ years old. Works just fine. No worries.