The songs on Sincerely come from three distinct recording periods: the band's first Tulsa and Los Angeles sessions for Shelter Records in 1974, which were intended by the label as rehearsals and demos but produced both of the first two singles (the top 20 hit "I'm on Fire" and "You Were So Warm"), a recording session produced by Robin Cable at Trident Studios in London that produced an entire album of material (tentatively called Fire), and the band's sessions in Tulsa after returning from London.

[3] Due to the split between Leon Russell and Denny Cordell, Shelter Records lost its distribution deal in 1975 and was essentially out of business for a year.

Had Fire been released as planned in late 1975, the track list supposedly included the following thirteen songs, with five songs produced by Oister (#) and eight by Cable (+): "I'm On Fire"#, "England"+, "Look Like An Angel"+, "I Don't Know My Name"+, "Lovin' Me"#, "Rock Yourself, Son"+, "Sky Blue"+, "Shark (In The Dark)"#, "Miserable Lady"+, "You Were So Warm"#, "No Resistance"+, "Dancer"+ and "Please Say Please"#.

Because of the shifting distributions of Shelter Records until it was acquired by EMI in 1993, Sincerely went out of print on LP within a couple of years after release.

However, all of the bonus songs on the 2007 Raven Records reissue were previously released on The Great Lost Twilley Album.