Who Really Said It? (If Anyone)

This story, repeated most recently in a New York Times profile of recently deceased writer Harold Bloom, famous for (among other things) his productivity, appeared earlier in a book by Jay Parini:

"The story circulates in academe that a graduate student once telephoned Bloom at home in New Haven.  His wife answered, "I'm sorry, he's writing a book."  "That's all right," the student replied.  "I'll wait."

This story, in which the caller is Alfred Hitchcock to prolific novelist Georges Simenon, is told in a recent profile of Simenon by Ian Tompson:

Simenon demanded silence as he set out to write one Maigret adventure a week. When Alfred Hitchcock telephoned one day, he was told: ‘Sorry, he’s just started a novel.’ ‘That’s all right, I’ll wait,’ came the reply.