The date range is established by the relationship between this letter and the letters from Arthur Nicols, 7 March 1871 and 11 March 1871 (Correspondence vol. 19).
See Correspondence vol. 19, letter from Arthur Nicols, 7 March 1871. Nicols had written about pet koalas (Phascolarctos cinereus) that acquired a taste for tobacco and rum.