The referenced research also considers the publications by Kay and his team (including his theses and the Smalltalk-72 and 76 manuals) and other uses of the term. I think Kay mixes things up in retrospective; in his 1968 thesis he used the terms "object language" and "object machine", but not "object-oriented"; imagine giving your new breakthrough method a name, but then not using that name anywhere in the publication; that seems unthinkable, especially with an accomplished communicator like Kay. The first time "object-oriented" appears in a publication of his or his team is in 1978.