A famous anecdote involves a visitor to a company with the owner. He noticed a rather unremarkable man at a desk doing apparently very little. He pointed him out to the owner.
The owner replied "That man once came up with an idea that saved the company thousands of dollars."

Survival books and instructors are much like that man. One book may hold one or two overlooked facts not found in others. The 2 oz. backpacker discussion on button compass accuracy is a classic.

All books have the potential of repeating 'fossilised' popular myth and error. The proliferation of solar still illustrations tells me a great many 'experts' have no true experience with the things.This is a danger, if, after reading 5 survival books promoting solar stills you accept them as truth.

And here the 'one good idea' becomes valuable if an otherwise standard guide says the solar still has no water and the emporers of such nonsense no goretex/buckskin/wool clothes.

Years ago a friend went on my advise to Reevis Mountain School.He was going to attend ASU for his graduate work and I suggested a survival class for his future field seasons.
My friend returned, and I heard a long complaint about the vegetarian fare, campfire talks of reincarnation and 'NEW AGE' atmosphere.
He then proceeded to show me, greatly excited his new mastery of friction fire starting, a skill I gave up showing him.
It seems, and subsequent students seem to confirm this, that Peter has a gift for teaching friction firemaking.

My friend is sitting there, catterwalling about reincarnation and he now possessed one of the most ancient and basic of survival skills.

Most of the literature and instructors are like an $8 Mora. They may not be the best, or highly regarded. But they are often enough adequate to get you back home.