I have left 120s-330s set, some for years, with no effect whatsoever. We had a long thread about storing set-vs-relaxed and an engineer on here posted technical information as well as some examples that completely refuted the idea of springs weakening while stored under tension for long periods of time.
Think about leaf springs, for example. They are always under a load, for YEARS. There are many examples.

Sam, you are both right and wrong:)

Something makes them weak, I have some 45 year old Victor 330’s that are really weak, and also some square jaw Bridgers 220’s you could set with one hand, but they still killed coon last I set them. But I am not an engineer, nor do I play one on TV.

Lol. This has held my curiosity for a while. I've had a Victor 330 stored with one spring set for about five years. So far the springs seem to be about the same strength. That makes me think that weakness is caused by repetitive use. But like you, I am no engineer.

Thats correct-repetitive use.
Guy Desrosier who makes the LDL trap told me it was the repetition not if they were stored with the springs hooked or not that weakened the springs over time..
A tiny knick from an axe or ice spud or from when the spring was made can lead to a broken spring in cold acidic water apparently on a set trap.

Kinda fits a wore out trap for a wore out trapper

Brother you got that right, think i need to take up a rocking chair before long, mind is wore out about as bad as body is.

Most of mine stay set year round, if a trap can't stand it's own springs to be set i don't keep it. Got some OLD blake and lamb longsprings still stought as the day they were off the factory line.
I think it's the cheaper quality material stuff is made with these days not the setting or not setting.

Craftsmanship and quality went out the window years ago.

Corrosion has a bigger influence on spring strength in the shorter time periods. And corrosion doesn't necessarily only come from being in water.

Number of cycles will effect strength over time, always a design compromise ... average number of stress cycles expected/time times the design life vs design stress along the fatigue stress curve for the material used. Depending on assumptions for an application.and costs, cycle count could range from a few thousand to several millions.

And yes, manufacturing issues, poor maintenance, environmental extremes, and/or a bad lot of material all have a way of compromising the real vs design stress limits and thus number of expected endurance cycles.