The idea expressed in the sentence from the last paragrap...

copy editors had to work in secret so that authors never knew that their writing would be adapted to what the publishers wished.

publishers did not want the public at large to realize that some well-know writers needed to have their work revised.

due to the formality of the English used at the time, most authors resorted to ghost-writers to help them with their work.

the language used in books and magazines was always revised to make sure it represented the ideal of acceptable English.

only standard English was adopted by writers and broadcasters, who all belonged to the higher levels of society.