Sources: StEdNL
- Olivia L. and Samuel L. Clemens to John Brown, 25–28 October 1875 · Hartford, Conn · UCCL01279 StEdNL
- Samuel L. Clemens to John Brown, 5 December 1876 · Hartford, Conn · UCCL02465 StEdNL
- SLC to John Brown, Jr., 1 June 1882 · Hartford, Conn · UCCL02212 StEdNL
- SLC per Olivia L. Clemens to William Blackwood, 7 November 1897 · Vienna, Austria · UCCL05311 StEdNL
- SLC to Francis H. Skrine, 7 January 1902 · Riverdale, N.Y · UCCL06224 StEdNL
- SLC to John Brown, Jr., 26 March 1906 · New York, N.Y · UCCL07402 StEdNL
- SLC to John Brown, Jr., 20 June 1908 · Redding, Conn · UCCL08036 StEdNL
- SLC to John Brown, Jr., 5 August 1909 · Redding, Conn · UCCL08438 StEdNL
- SLC to John Brown, Jr., September 1909 · Redding, Conn · UCCL08447 StEdNL
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