Short answers, pulled from the story.
The rehearsals for the Let It Be project started on the 2nd of January 1969. These sessions were part of a planned television documentary showcasing the Beatles' return to live performance.
John Lennon suggested the rooftop concert according to Billy Preston's recollection. The four Beatles and Preston arrived on the roof around 12:30 pm on the 30th of January 1969 to perform.
The Get Back album was shelved because the Beatles recorded Abbey Road and wanted to issue that album instead. Paul McCartney stated he wanted a divorce from the group on the 20th of September 1969, leading to the project being abandoned by December.
Phil Spector added orchestral and choral accompaniment to The Long and Winding Road which contradicted McCartney's conception of it as a simple piano ballad. McCartney was dissatisfied with this treatment while John Lennon defended Spector's work in his Rolling Stone interview.
Glyn Johns omitted Teddy Boy from the playlist since the song did not appear in the film and added Across the Universe and I Me Mine. I Me Mine was newly recorded on the 3rd of January 1970 with Harrison, McCartney, and Starr performing since Lennon had already left the band.