Very interesting to know what Christopher Tolkien assisted with, without actually having his name on the book, or as editor. Ie, I had no idea that he had any input on A Secret Vice (well, aside from his role with the Estate which could include reviewing it and saying "this is sanctioned by the Estate.")

This is apocryphal until I can dig up a primary source quote somewhere, but I am pretty certain that Christopher had massive input on the book (asking for a complete rewrite of the first draft, if memory serves). I will see what I can dig up (or will correct this post if I find I remembered incorrectly).

Material I have been able to dig up:

Although we toyed with the idea of presenting the ‘Essay on Phonetic Symbolism’ first, in order to reproduce the order of the folder, following feedback from Christopher Tolkien we gave prominence to ‘A Secret Vice’

From http://dimitrafimi.com/2016/06/29/res ... ing-tolkiens-secret-vice/

We were also very pleased (and quite nervously astounded!) that Christopher Tolkien took a special interest in this volume and contributed some incredibly helpful notes and comments to our original draft.

From https://www.tolkiendil.com/tolkien/interview/fimi_et_higgins_en

Co-editing Tolkien’s own words with [Andrew Higgins], with Christopher’s permission, has been one of the highlights of my career, + his comments on A Secret Vice made this book so much better.

From https://twitter.com/Dr_Dimitra_Fimi/status/1218067521749897217?s=20