There's a new interview with Cushman at Trek Movie
He repeats his version of 'The Alternative Factor,' but still doesn't provide a source.
He says quite a bit more about the ratings, but it seems more apparent than ever that he doesn't know what he's talking about (there were only two ratings services in the '60s and '70s?).
Probably the most revealing thing about Cushman is when he says, "Lucille Ball lost her studio because she sponsored Star Trek
, and was determined to put it on the air." That kind of thing is rather indicative of what you'll find in these books in that it both exaggerates the importance of the series and totally ignores important things that were happening outside of it in Hollywood.