A root for “brother” that Tolkien introduced in notes on finger-names from the late 1960s as a companion to √NETH “sister” (VT47/14, 26, 34). It conflicts with, and possibly replaces, earlier uses for √KHAN such as √KHAN “back” in notes from around 1959 serving as the basis for the prefix Q. han- in hanquenta “answer” (PE17/166). The root ᴹ√KHAN also appeared in The Etymologies of the 1930s glossed “understand, comprehend”, with various derivatives in both Quenya and Noldorin of similar meaning (Ety/KHAN).
It is unlikely that all these uses of √KHAN coexisted, but I think at a minimum both √KHAN “brother” and ᴹ√KHAN “understand, comprehend” should be retained for the purposes of Neo-Eldarin, as the latter has no good replacements in Tolkien’s later writing. As for hanquenta “answer”, it might be reinterpreted as “a saying providing understanding”, and so be derived from ᴹ√KHAN “understand”.
The root √THER or √SER “saw” appears in a discussion of the name Q. Vairë “Weaver” probably from the late 1950s, with Tolkien preferring √THER because it could be a variant of √TER “pierce” (PE17/33). That section of the discussion was rejected (PE17/34), but given Tolkien’s later use of †Þerindë > Q. Serindë “Broideress” or “Needlewoman” as a sobriquet for Fëanor’s mother Q. Míriel (MR/185; PM/333), it seems √THER “sew” survived. This root could be a later iteration of ᴱ√SERE “twine, tie, bind” from Qenya Lexicon of the 1910s with derivatives like ᴱQ. serma “string, cord” and ᴱQ. serta- “tie” (QL/83); its Gnomish derivatives in the contemporaneous Gnomish Lexicon such as G. ther- “tie” and G. theres “ribbon” make it clear the actual early root was ✱ᴱ√ÞERE (GL/72).