I can't speak for any substance you may have in your collection, but if you haven't noticed any significant pressure release when opening such a bottle, it means you're safe. And yes. pressure doesn't increase indefinitely. There's always an equilibrium point where decomposition of a substance cannot occur unless pressure drops.
I hope you're not storing liquified gases, ok?
An example of a solution that may give you an idea how tough these containers are is carbonated water. Fill it up, slosh it around, heat it up and look for damage. I bet it will be just fine.
If storing something particularly unsafe use a deformable container such as HDPE. It will give you a good idea of pressure inside just by feeling it in your hand.