17 September 1931: birth of Ian Fairbairn, who played Questor in The Macra Terror (Second Doctor, 1967), Mark Gregory in The Invasion (Second Doctor, 1968), both John Bromleys in Inferno (Third Doctor, 1970) and Chester in The Seeds of Doom (Fourth Doctor, 1976).
17 September 1957:
17 September 1972: death of Peter Stephens, who played Cyril, the Kitchen Boy, and the Knave of Hearts in The Celestial Toymaker (First Doctor, 1966), and Lolem the high priest in The Underwater Menace (Second Doctor, 1967).
17 September 2010: death of Louis Marks, author of Planet of Giants (First Doctor, 1964), Day of the Daleks (Third Doctor, 1972), Planet of Evil (Fourth Doctor, 1975) and The Masque of Mandragora (Fourth Doctor, 1976).
ii) broadcast anniversaries
17 September 1966: broadcast of third episode of The Smugglers. Ben and Polly use witchcraft to escape the villagers, but are recaptured; the Doctor fails to escape the pirates. I should have mentioned previously that Elroy Josephs, as Jamaica, is the first Afro-Caribbean actor to have a speaking role on Doctor Who.
17 September 1977: broadcast of third episode of Horror of Fang Rock. People start dying; Reuben starts glowing; and the Doctor admits to Leela that he has locked the enemy in rather than out.
17 September 1993: broadcast of fourth episode of The Paradise of Death on BBC radio. Some very weird stuff with tame giant bats.
17 September 2011: broadcast of The God Complex. The Eleventh Doctor, Amy and Rory explore a hotel with some very odd residents.
iii) date specified in-universe
17 September 2016: the Level Two Careers Fair takes place at Coal Hill School, as seen in 2016 Class episodes For Tonight We Might Die and Co-Owner of a Lonely Heart.