i) births and deaths

12 May 1968: birth of Catherine Tate, who played Donna Noble in New Who from 2006 to 2010.

12 May 2001: death of Norman Kay, who composed the incidental music for An Unearthly Child (1963), The Keys of Marinus (1964) and The Sensorites (1964).

ii) broadcast anniversaries

12 May 1973: broadcast of sixth episode of Planet of the Daleks. The Doctor, Jo and the Thals trap the Daleks in the ice volcano.

12 May 1996: first broadcast of Doctor Who: The Movie on a local cable channel in Edmonton, Canada. Canonical release date is 14 May so I'll do the picture then.

12 May 2007: no Doctor Who episode shown today, the series taking a break for the Eurovision Song contest between The Lazarus Experiment and 42. The winner was the Serbian entry "Molitva", which lays its cards pretty clearly on the table.

iii) date specified in canon

12 May 1999: birth of Adelaide Brooke, who we meet in The Waters of Mars (2009).