ALAN GRANT: When I finally got hold of Denny, he explained that my stories hadn't been so good for the past year or two. I asked why he, as my editor, hadn't pointed this out a year or two earlier and saved me a lot of grief? He had no reply.
The likely answer is that O'Neil wasn't actually editing the book in the first place. From what I've heard over the years, Denny basically let his assistants do all his work for him.