31 January 1970: broadcast of first episode of Doctor Who and the Silurians; first appearance of Bessie. The Wenley Moor nuclear research centre is suffering from unexplained deaths and a tyrannosaurus in the basement.
31 January 1976: broadcast of first epsiode of The Seeds of Doom. A mysterious pod is found in Antarctica; it opens, infecting a nearby scientist. The Doctor and Sarah come to investigate.
31 January 1981: broadcast of first episode of The Keeper of Traken. First appearance of Sarah Sutton as Nyssa, and of Anthony Ainley though not yet as the Master. The dying Keeper invites the Doctor to come to Traken, where social balance is threatened by the evil calcified Melkur.
ii) date specified in canon
31 January 2007: the SS Elysium arrives in Panama after its encounter with Cybermen, as told in David Banks' 1993 novel Iceberg.
That brings January to an end, much the heaviest month in this project with 107 Old Who anniversaries, five Torchwood, one each of Sarah Jane Adventures and New Who, and various other things to take into account. February and March are also fairly intense; April and May (where many Old Who seasons had finished, and the numbers are not quite balanced out by the start of New Who) less so, and June will be a welcome relief.