This thing about springs taking a set is sorta like velocity and barrel length, or a rifle bullet's shape and its "brush bucking".
From another thread on pistol magazine springs: Spring steel, if it is indeed spring steel, doesn't take a set in normal deformation from its free length. Any good quality spring will deform to some design condition and happily return to its free length, no matter how long it has been compressed. It can, of course, be fatigued by millions of repetitions.
Shift to cars: Assume a collector car, used rarely. When the engine is off, some of the springs will be at full compression, and may be so for years. But they fire up and seem to run fine...
In all my years in car racing, I never had degradation of valve springs. 15 races in a season, with 120 minutes per weekend, averaging, say, 2,000 cycles per minute of a valve-spring. What's that, 3.6 million?