Like I said, those are MY definitions, and I have no doubt that others have different definitions.
None of this is cast in stone, it is all probabilities and reductions of risk. The difference in s played guitar being tuned to pitch for 40 years is that you do not really want to be tuning and detuning the guitar constantly, if you are using it regularly. The costs of replacing strings due to metal fatigue in that example would be prohibitive, even compared to a neck reset. Sitting unplayed in a case means having it detuned/unstrung once, and not retuning it constantly, so the costs of a potential neck reset outweigh the costs of string replacement. With the guitar detuned/unstrung, there is none of the string tension to cause the neck angle to change or other string tension related structural problems.
Another way to think if it is this way: Take 2 brand new guitars. Put them in their cases, one strung to standard pitch, and the other with no strings at all. Wait 25-30 years without touching either guitar. Which do you think will need a neck reset after the 25-30 years are up? Now, think if why the strung to tension guitar needs a neck reset.
As for your guitars that have sat unplayed, they may have not been damaged. It is also possible that they may have. You won't know until such time as a repair is required that a glue joint failed inside the guitar. Your guitars may never have such a failure, or they may already have failures like this. Keeping the tension on the guitars that are not being played constantly just increases the stress on the entire instrument, but does not automatically mean the problems will occur. I prefer to err on the side of caution, and remove the strings on any guitars that I don't use regularly. You are free to do as you wish. As I said repeatedly in my post, these are my guidelines, and I am sure that others have theirs. Feel free to check with your trusted luthier regarding this, or any other matter.
In human terms, think if it this way: When you are working as a bricklayer, you may need to haul 150-170 lbs of bricks from the brick pile to the brick wall that is being built (analogous to a regularly played guitar). I don't know of anybody who would just walk around with an extra 150-170 lbs strapped to his back (analogous to an unplayed guitar). In both cases, there is no reason to carry the weight (in the case of the bricklayer) or tension (in the case of unplayed guitars) if it doesn't serve a purpose. In the case of unplayed guitars, detuning a guitar involves a couple of revolutions of a tuning knob. For me, that is something that I am fine doing. You are free to do as you wish. You can put heavy strings on, tune the guitars to higher than concert pitch, and leave them on the rear deck of a car in the middle of a hot summer day. Your money, your choices, not for me to make decisions for you.
Kostas