TCG Letter #640 / Carpenter Letter #267

The Letters of J.R.R. Tolkien (1981), pp. 353-54, p. 451 (Carpenter note)

The Letters of J. R. R. Tolkien: Revised and Expanded ed. (HarperCollins, UK), pp. 493-95, p. 632 (Carpenter note)

The J.R.R. Tolkien Companion and Guide - Chronology (2017), p. 661

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

Cartas de J.R.R. Tolkien, pp. 503-4, p. 644 (notas de Carpenter)

J.R.R. Tolkien: Life and Legend, p. 14 (item 15 quotes from Tolkien's letter and shows a drawing of Hilary's from 1904)