2012 ‘Rock on (and on) (and on): The never-ending Fifties Revival’ http://retromaniafootnotes.blogspot.ie/2012/05/800×600-normal-0-false-false-false-en_7061.html
current versus catalogue (oldies) music on sale
2015 marked an interesting milestone in the history of the U.S. music industry. For the first time ever, current releases accounted for less than half of total album sales in the United States as catalog albums outsold new releases by more than four million units. Nielsen defines catalog releases as any release older than 18 months, thus including old Beatles albums as well as more dated releases of current artists.