I guess they just assume that we know that some of those albums sales ARE from 2003/04 like Linkin Park's 'Meteora' whereas others are from furthur back eg Shakira's 'Laundry Service' (from 2001). So they're just like distinguishing or making it clear to us when the cumulative sales (for each album) are from.
Bomb's sales this week at Mediatraffic : I'll stick with 38,000