TCG Letter #583 / Carpenter Letter #209

The Letters of J.R.R. Tolkien (1981), pp. 267-70

The J.R.R. Tolkien Companion and Guide - Chronology (2017), p. 554

Cartas de J.R.R. Tolkien, pp. 396-9

The Letters of J. R. R. Tolkien: Revised and Expanded ed. (HarperCollins, UK), pp. 386-89

Error in hardcover and Kindle editions: it _improbably_ formally related to > it is _probably_ formally related to p. 388

J.R.R. Tolkien A Descriptive Bibliography, Di1, p. 350