Dating protocol

Due to the various temporal discrepancies in the 1970s and 1980s, a dating protocol was created by the United Nations for their files. It was established in January 1990 at a secret meeting in Geneva between Alistair Gordon Lethbridge-Stewart, Charles Crichton, and Amara Essy, (PROSE: The Enfolded Time) following an encounter between the Doctor and a displaced time traveller. (AUDIO: The Web of Time)

According to one account, the after-effects of a temporal shockwave which caused the 1960s to coincide with the 1970s continued to create inconsistent chronology for nearby time travellers after the Seventh Doctor dealt with the disturbance. He remarked that he'd always wondered how someone could have retired in the 1970s after having worked in the 1980s, and theorised that these after-effects were to blame. (AUDIO: The Split Infinitive) Another anncount claimed the Doctor himself was to blame for causing the damage with his frequent visits to the time period in his faulty TARDIS by non-corporeal temporal maintainers The Accord. (PROSE: The Enfolded Time)

Events covered by the protocol
A number of events were filed as occurring at two different equally valid dates during the years covered by the protocol:
 * The Great Intelligence's invasion of London (TV: The Web of Fear) occurred in February 1969 and March 1975. (PROSE: The Enfolded Time)
 * The dinosaur invasion of London (TV: Invasion of the Dinosaurs) occurred in 1974 and 1979. (PROSE: The Enfolded Time)
 * The attack on an environmental peace conference by Zygons occurred in both the 1970s and the 1980s. (TV: Terror of the Zygons, The Day of the Doctor)
 * Brigadier Lethbridge-Stewart retired from UNIT in both 1976 (TV: Mawdryn Undead) and 1981. (PROSE: The Enfolded Time)

Behind the scenes
The United Nations dating protocol is a reference to the UNIT dating controversy, a source of interest and argument among writers and fans.