Complex sentence: Since it is known that Burnett was born in 1883, married in 1905, and blinded in 1907, and the second stanza of "Farewell Song" mentions that the singer has been blind six years, which put the date at 1913.
Split into simpler sentences: Since it is known that Burnett was born in 1883, married in 1905, and blinded in 1907, the dating of two of these texts can be made on the basis of internal evidence. The second stanza of "Farewell Song" mentions that the singer has been blind six years, which put the date at 1913.