The central theme of 2 Years On is undoubtedly Lonely Days. This song was released as the album's first single and had an excellent reception in the United States, reaching number 3 on the Billboard Hot 100 and number 1 on the Cashbox chart. In the United Kingdom, however, its success was more moderate, reaching number 33. Although the album itself reached number 32 on the US charts, the songwriting reveals a particular dynamic: only three tracks credit the three Gibb brothers as composers: the aforementioned Lonely Days, its B-side Man For All Seasons, and Back Home. Maurice Gibb provides vocals on all tracks, while Barry Gibb and Robin Gibb only participate in those they wrote or co-wrote.
The story behind the Bee Gees' reunion for this record is interesting. In March 1969, Robin Gibb had announced his departure, releasing a successful solo single. By August, drummer Colin Petersen was fired, and the band completed the album Cucumber Castle. Before its release, Barry and Maurice Gibb announced the group's dissolution in December 1969, even releasing singles separately. However, in June 1970, Robin and Maurice decided to reunite, supported by Geoff Bridgford. They recorded several songs, some of them re-recordings of previous material. By August, they announced the return of the Bee Gees, with or without Barry, and recorded fourteen tracks. Finally, on August 21, the three brothers came together to continue recording, with Barry Gibb declaring that "the Bee Gees are here and will never, ever break up again."