I don't have any empirical evidence outside of having collected, stored and aged wine for.. 30 years now. But my gut feeling, is that like wine, storage conditions are EVERYthing. Cool, dark, and minimum exposure to air most likely will play a dramatic role.
My in-rotation and soon to be opened bottles stay in the cellar. Temp controlled at 55F. I have NEVER had a bottle taste "too old", and some have reached a year and a half.
Now I'm stockpiling for Vapeocalypse. THOSE are going in the deep freezer, unopened. SOME flavorings theoretically could experience precipitation of some components, but I am relatively comfortable, that warming back to normal temp and vigorous shaking will reblend. 3 year old, unopened PG/VG 100mg nicotine from said freezer, is in perfect shape. I have no reason to believe that the same mix, plus flavorings, would be any different.

my 2cents.
Oh, and the Cloupor
thread finally reached 100K posts. With that, I am retiring back to my home here, if you all will have me..