Earth's timeline

The Time Lords understood that the planet Earth had a unique timeline.

The 1986 Cyberman invasion of Earth was seen by the Time Lords as a temporal anomaly which was not part of their orthodox vision of Earth's history — and the Doctor's presence on Earth at the time, in his first incarnation, led to the speculation that he had somehow bent the planet's time-stream out of shape himself, permitting the invasion. Less harshly, it was suggested by the prosecution for the Second Doctor's trial that the Doctor may have accidentally "ripped" the Earth's time stream in the 20th century by operating his TARDIS there too often. The Doctor convinced the prosecution that this line of argument was misguided by pointing out that if excessive TARDIS activity really had deleterious effects on a nexus world's time-field, Gallifrey itself would long have been "a smoking hole in space". (PROSE: The Cyber Files) Elsewhere, however, the Accord were aware that Earth's timeline was damaged by the TARDIS as a result of its unique faults. (PROSE: The Enfolded Time)

During the multiverse collapse, Earth's timeline was massively destablized by the company Good Times offering time travel tours to every point in history, thus commercially sanitizing every culture at every point in time. (PROSE: The Last Resort)

During the Last Great Time War, the Time Lords used the Matrix to project the post-Time War universe and thus foresaw Big Bang Two, which they knew would cause subtle changes in Earth's timeline resulting in the memory of high-profile alien incursions such as the 2009 Planetary Relocation Incident being forgotten, such that humanity at large would remain unfamiliar with the Daleks as evidenced during the later Security Drone Incident of 2021. (PROSE: Dalek Combat Training Manual)