8 April 1942: birth of Lovett Bickford, director of The Leisure Hive (Fourth Doctor, 1980)
ii) broadcast anniversaries
8 April 1967: broadcast of first episode of The Faceless Ones. The Doctor, Ben, Polly, and Jamie land at Gatwick Airport to get mixed up in an affair of vanishing corpses; Polly is apparently brainwashed.
8 April 1972: broadcast of first episode of The Mutants. Geoffrey Palmer is the best thing in this story and he gets killed before the end of this episode; five more to go, folks...
iii) dates specified in-universe
8 April 1809: birth of Joseph Sundvik
8 April 1969: setting of The Impossible Astronaut (Eleventh Doctor, 2011)