Do they only count CD sales, or does “CD sales” include downloads?
Digital download counts, but downloads of singles (just like in the days of 45s) won’t count for albums. Which is probably what’s killing the album sales. The pop record formula of 3 or 4 good songs and filler doesn’t work well with so many ways to just get the songs you want. Used to be they’d “protect” one or two songs so people had to buy the album, now that’s not possible.
Just CDs; those little plastic discs that young people have absolutely no use for, if they even own a device that would play one.
By comparison, Adele's 25 last year sold more downloaded copies on the first day of release in the United States alone than this Mozart CD sold.
These days, only old people buy CDs.