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.