i) births and deaths
23 July 1992: birth of Tosin Cole, who plays the Thirteenth Doctor's companion Ryan Sinclair (2018-present).
ii) broadcast anniversaries
iii) dates specified in-universe
23 July 1790: setting of the first two episodes of the story we now call The Reign of Terror (First Doctor, 1964)
23 July 2012: Jane McKillen disappears from Dame Kelly Holmes Close, as seen in Fear Her (Tenth Doctor, 2006).