6 March 1965: broadcast of "Crater of Needles", fourth episode of the story we now call The Web Planet. Ian and Vrestin meet the Optera; Barbara tries to link with the invading Menoptera but they are massacred by the Zarbi.
6 March 1971: broadcast of sixth episode of The Mind of Evil. The Thunderbolt missile and the Keller machine are both destroyed, but the Master escapes.
6 March 1976: broadcast of sixth episode of The Seeds of Doom, ending Season 13. The Krynoid grows to enormous size but is destroyed by the RAF.
ii) date specified in canon
6 March 2005: setting of Rose, according to poster seen in Aliens of London (2005).