Sources: NNWH
- Samuel L. Clemens to the Public, 21 November–6 December 1875 · Hartford, Conn · UCCL10433 NNWH
- SLC to Karl and Hattie J. Gerhardt, 11–19 April 1881 · Hartford, Conn · UCCL01935 NNWH, ViU
- Players Club to SLC, 10 November 1904 · New York, N.Y. · UCLC39140 NNWH
- SLC to Robert Reid and Players Club members, 11 November 1904 · New York, N.Y · UCCL06950 NNWH
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