10 April 1954: birth of Glen McCoy, writer of Timelash (Sixth Doctor, 1985) and the first writer of colour to write for televised Who (I think also his novelisation is the first Who book by a writer of colour).
ii) broadcast anniversaries
10 April 1965: broadcast of "The Wheel of Fortune", third episode of the story we now call The Crusade. Barbara remains a captive; the Doctor is forced to reveal Vicki's true gender.
10 April 1971: broadcast of first episode of Colony in Space. The Time Lords send the Doctor and Jo to a colony planet where the Doctor is attacked by a robot. As usual with a Malcolm Hulke story, there are green lizard people.
10 April 2010: broadcast of The Beast Below. In the 33rd century, all of the United Kingdom's citizens (apart from the Scots) live onboard Starship UK, searching for a new home amongst the stars as the Earth is being roasted by solar flares. What is going on? What secrets does Starship UK hold at its depths, and who is hiding them? Soon, the Doctor is forced to make an impossible choice.
iii) date specified in-universe
10 April 2013: Clara Oswald receives a letter from Madame Vastra while attempting to bake soufflés. It contains an invitation to an emergency psychic conference call with herself, Jenny Flint, River Song, and Strax.