17 July 1925: birth of Hugh David, who directed The Highlanders (Second Doctor, 1966-67) and Fury from the Deep (Second Doctor, 1968). As an actor, he was one of those approached about playing the role of the Doctor back in 1963, but turned it down.
ii) broadcast anniversaries
17 July 1965: broadcast of 'Battle of Wits', third episode of the First Doctor story that we now call The Time Meddler. The Monk is luring the Viking fleet to attack; and Steven and Vicki discover, to their amazement, that he has his own Tardis.
iii) dates specified in-universe:
17 July 1987: In the first chapter of the 1996 Seventh Doctor novel Damaged Goods, by Russell T. Davies (later the first showrunner of New Who), Simon Jenkins, known as the Capper (because, it was said, he first kneecapped someone at the tender age of fourteen) sets fire to himself and dies. But he does not stay dead.
17 July 2006 (?) was the release date of both The Pink Panther and Date Movie, at least according to advertisements in a Cardiff supermarket in the 2006 Torchwood episode Out of Time, which is odd because the episode is explicitly set in December.