The Guardian, however, is a bit of a problem. Harlan Ellison’s unused drafts included The Guardians of Forever, three ancient beings who controlled time. The finished episode, heavily rewritten by writers other than Ellison, has The Guardian (singular) of Forever, a mysterious, donut shaped time portal. It is an extrapolation of the original three beings, but NOT the three beings. Harlan introduced a concept which evolved by others into something else in the final episode. And THIS is the concept you see marketed and written about.
See Art Buchwald versus Paramount, regarding "Coming to America," where a vague 'treatment' was considered so vital to the end product he won millions.
Moreover, Harlan Ellison's own second draft, which had McCoy bit by a "rabid" animal rather than accidentally injected, featured the singular, donut time portal Guardian. So it's still his creation.
Pieces of the second draft are in the White Wolf edition of the original script.