I've wondered about this as well. There is a common debate in the firearm community about leaving magazines loaded thereby leaving the spring inside the magazine compressed versus leaving them unloaded and leaving the spring relaxed. The general consensus is that leaving the spring compressed isn't what weakens the spring, its the loading and unloading, constantly compressing and relaxing the spring. Also, if you think about taking a metal rod, such as a straightened out wire clothes hanger, put in a vise leaving about 12" free. If you lightly press down and release, the wire will bounce back and not have any change in shape, but if you bend it too far it will pass its point of elasticity and will not go back to the original place. So with the magazine spring above, theoretically as long as you never compress the spring tighter than its "point of no return", it should never weaken. In my opinion regarding down, what causes it to lose its fluff is the bending and breaking of the feathers (not counting other things such as moisture), so as with the examples above, the more you compress and relax it, and the tighter you compress it, the more damage will occur. I don't think the amount of time it is compressed has any relevance. I wouldn't worry about something being compressed from the factory, regardless how long its been that way. You will do a lot more "damage" from normal use of packing and unpacking.