Here’s an interesting statistic from Paul Grein from Yahoo Chart Watch:
The albums on The Billboard 200 this week accounted for 1,682,000 in sales. […] Sales of all “current” albums (those charted and those that didn’t chart) totalled 2,734,000 this week. The other 2,429,000 albums sold this week were catalog. (Those two figures add up to 5,163,000.)
It’s interesting enough that catalog sales represent almost half of total sales for the week. But even more fascinating is what a small percentage of total album sales the Top 200 represents: only about one-third of all album sales for the week. Two-thirds of the week’s album sales are outside of the Top 200.
Even looking at the “current” releases, that leaves 1.1 million current albums outside of the Top 200, or about two-fifths of total sales of current music. That’s a big chunk of low-sellers!