Question: What is a compilation album of previously unreleased songs and alternate takes recorded 1969–1980 by American singer-songwriter, who was one of the most popular acoustic artists of the decade and one of its best-selling artists?
Sentence (from "10th Anniversary: Rap-a-Lot Records"): 10th Anniversary: Rap-A-Lot Records is a compilation album released by Rap-a-Lot Records to celebrate the label's tenth anniversary.
Relevant evidence: No