11 December 1945: birth of Zienia Merton, who played Ping-Cho in Marco Polo (1964) and the registrar in The Wedding of Sarah Jane Smith (2009), a 45-year gap between appearances in Who and its spinoffs which is unlikely to be repeated.
ii) broadcast and webcast anniversaries
11 December 1966: broadcast of "Counter Plot", fifth episode of the story we now call The Daleks' Master Plan. Sara, the Doctor and Steven are transported to Mira and menaced by the invisible natives before being captured by the Daleks.
11 December 2003: webcast of fifth episode of Scream of the Shalka. The Shalka activate the other sleeper communities and the end of the world draws nigh.