100% reliable info on growing orchids in a 1985 book?

[Val]

Looking for books on growing orchids, I've read a very high recommendation of a book published in 1985.

On the other hand, doing research on the Internet, I noticed that some basic rules that used to be taken for granted have been proven wrong by relatively recent scientific research. For instance, it's not high Phosphorus fertilizers that help/induce blooming, but low Nitrogen ones.

Hence my question: how "fresh" must a book be in order to be free of outdated info?