They can develop bends or deflections from fretting pressure and settle at the break angles. As a bassist on a budget, I got in the habit of loosening my strings now and again and flipping the ball end 180 degrees which would reinvigorate the overtones a bit.
I like the sound of new strings on guitars though, especially strings that have been on the instrument a few days, in played, the Goldilocks moment. That's effed up I know. So what.