I've owned several acoustic guitar over the last 50 years and guitar tone changes over time, based on how much music it hears/makes. If you take a midrange guitar and put it on a stand near a speaker, and subject it to moderately loud music for days on end the sound _does_ change for the better. This is a commonly observed affect. Other guitarists have mentioned it to me.

Now maybe op didn't word the physics and material science precisely, but what they describe is real. Perhaps you have a better explanation for a commonly observed phenomena.