1 August 1929: birth of John Flint, who played William des Preaux, a knight loyal to King Richard, in the story we now call The Crusade (First Doctor, 1965) and also Urquhart, the Concorde pilot in Time-Flight (Fifth Doctor, 1982).
1 August 2008: death of Gertan Kauber, who played the dimly seen galley-master in the story we now call The Romans (First Doctor, 1965) and Ola in The Macra Terror (Second Doctor, 1967).
ii) broadcast anniversary
1st August 1964: broadcast of "A Desperate Venture", the sixth and final episode of the series we now call The Sensorites. Barbara reappears (after several weeks' holiday) and sorts out the Sensorites; meanwhile the Doctor and Ian have tracked down the deranged astronauts in the tunnels. So everyone's a winner! Except the Second Elder and the Engineer, of course. This is the episode where Susan says, of her home planet,
at night the sky is a burnt orange, and the leaves on the trees a bright silver.Ends on a dramatically sour note as the Doctor takes offence at Ian and promises to put him and Barbara off at the next landing.
iii) date specified in-universe
From the 1999 Eighth Doctor novel Unnatural History, by Jonathan Blum and Kate Orman:
Dad sighed his I-know-Tm-right-sweetheart sigh. ‘We thought it was a practical joke at first. But they kept coming.’
‘What?’ Sam stared at the stack of cards in his lap. ‘How many?’
He handed her another card, and another, postmarked from all around the world. San Francisco. Auckland. A letter dated London 1894, with ‘Do not deliver until 1 August 1997’ written on it.