There is no evidence that English historically used ‘they’ to refer to a named and known individual.
For centuries, the English language has used ‘they’ as an epicene pronoun (i.e. to mean ‘he or she’). This epicene use is shared by authors from Shakespeare to Austen and Shelley .
However, epicene use of ‘they’ rules out knowledge of the identity — and thus the sex — of the person in question. In other words, this historical use of singular ‘they’ is restricted to contexts where ‘they’ refers to an unknown party, rather than to a particular named and known individual.
There is no literature on the use of definite singular ‘they’ (i.e. to refer to a named and known person) before 2017 .
Furthermore, the research undertaken in 2017  indicates that many English speakers who naturally use epicene ‘they’ find it difficult to parse uses of ‘they’ to refer to a named and known singular individual.
 Grubber, B. (2017). Singular They: The Best Epicene Pronoun. Student Research Conference Select Presentations: Paper 45. [Link]
 Konnelly, L. & Cowper, E. (2020). Gender diversity and morphosyntax: An account of singular they. Glossa: a journal of general linguistics 5 (1): 1–19. [Link]
 Bjorkman, B.M. (2017). Singular they and the syntactic representation of gender in English. Glossa: a journal of general linguistics 2 (1): 1-13. [Link]