Music buyers must have been feeling sentimental last year, because according to Nielsen SoundScan's year-end music report, old albums outsold new releases by 4.3 million copies, as reported by Chart Attack. Old music, also referred to as a "catalog" song or album, is defined in the report as anything released more than 18 months ago. This discrepancy between old and new sales marks the first time that this has ever happened in the music industry.

Nielsen states that while newer albums did win out in digital sales, older albums kept the lead in physical copies sold, and older songs accounted for nearly 70 percent of all on-demand streams. The stats are especially surprising considering that 2015 saw a blockbuster release from Adele. Even though her album, 25, came out late in the year, it managed to post up some impressive numbers, accounting for 3.1 percent of all album sales for the year and becoming the 61st best-selling album in Nielsen SoundScan history within just six weeks of being released.

Luckily for an artist like Adele who has a couple other releases to her name, she benefited from the catalog stats as well: In addition to people buying her latest album, they also went back and bought her older albums, 21 and 19, pushing her total sales to 8 million albums in 2015.