Tolkien used a number of similar roots for “bay” but their exact form varied over his life. The earliest form was ᴱ√KOPO “keep, guard?” (the question mark is Tolkien’s) from the Qenya Lexicon of the 1910s with the derivative ᴱQ. kópa “harbour” (QL/47). This root and its Qenya derivative were linked to words like G. gob “hollow of hand” and G. gobos “haven” in the contemporaneous Gnomish Lexicon (GL/40). Given these Gnomish forms it is likely the true root was ✱ᴱ√GOPO since initial g- became k- in Early Qenya. In Early Noldorin word lists from the 1920s, however, the related word became ᴱN. cú “bay, cove” < ᴱ✶kópa (PE13/141).
The root ᴹ√KOP appeared in The Etymologies of the 1930s, but Tolkien seems to have abandoned it in favor of ᴹ√KHOP, changing ᴹQ. kópa “harbour, bay” to ᴹQ. hópa/N. hûb “haven, harbour, small landlocked bay” (Ety/KHOP, KOP). In draft maps for Gondor from the 1940s, however, Tolkien gave N. Cobas “Haven” (TI/312, WR/434). Finally, in notes from the late 1960s Tolkien had S. côf “bay” in Côf Belfalas, the Sindarin name for the “Bay of Belfalas”, though the paragraph where it appeared was struck through (VT42/15). As suggested by Carl Hostetter, côf was probably derived from a variant of earlier ᴹ√KOP (VT42/29 note #36), perhaps ✱√KOB.
Thus it seems the conceptual evolution of this root was 1910s ✱ᴱ√GOPO >> 1920s ᴱ√KOPO >> 1930s ᴹ√KHOP >> 1940s ✱ᴹ√KOP >> 1960s ✱√KOB. Given Tolkien’s extreme vacillations on the form of this root, it is probably best avoided for purposes of Neo-Eldarin, but if you do use it I recommend sticking with the derivatives of 1930s ᴹ√KHOP, since those are likely most recognizable to readers of Elvish.