2164

2164 was the date on a calendar found by Ian Chesterton upon arriving in the 22nd century. He went on to suggest it looked like it hadn't been changed for some time and so it was unlikely to be the actual date. (TV: The Dalek Invasion of Earth)

Behind the scenes

 * In NOTVALID: Whatever Happened to Susan Foreman?, Susan Foreman claims that 2164 was infact the year in which the 22nd century Dalek invasion was launched. Having been defeated on Skaro by the Thals led by Ian Chesterton, the Daleks used their own TARDIS to travel into the past with the intent to wreck revenge on Ian's people or, better still, prevent Ian himself from being born. However, they were unable to go any further back than 2164 due to a leak in their fluid link.
 * The Discontinuity Guide also claimed that "mankind's first major encounter with the Daleks", following the earlier Vulcan Incident, took place in 2164. It is further noted that, since the Fourth Doctor inadvertently changed Dalek history so that Davros survived, this event would have occurred vastly differently if it happened at all in the new timeline.