31 July 2004: death of Robert James, who played Lesterson in The Power of the Daleks (1966) and the High Priest in The Masque of Mandragora (1976)
ii) broadcast anniversaries
iii) date almost specified in canon
31 July 1977: the latter part of episode 3 and all of episode 4 ofImage of the Fendahl (1977) are set on a day specified as 'Lammas Eve' (the day before 1 August, ie 31 July) by Mrs Tyler. There is no reason to suppose that the year is other than 1977.