Unthinking Modernity: Innis, McLuhan, and the Frankfurt School by Judith Stamps (1995):

McLuhan had not read Havelock at the time of writing The Gutenberg Galaxy… (129)

Since McLuhan referred to Havelock’s 1951 Crucifixion of Intellectual Man a decade before The Gutenberg Galaxy, this is clearly false. And there is much indirect evidence indicating that he read Havelock’s 1946-1947 essay in Phoenix, as well as his 1948 review in UTQ, as they appeared.

But Stamps seems to have used ‘McLuhan had not read Havelock’ here as a stand-in for ‘McLuhan had not read Havelock’s 1963 Preface to Plato‘ which, in reference to the 1962 publication of The Gutenberg Galaxy, is vacuously true.