The B2 creates the discid and toc files when it rips a CD. The toc [Table of Contents] is, I think, a list of track start positions, and the discid is the calculated value that is used to look up the dic in the online databases. Most ripping software doesn't write this info to disc; it's not needed after the disc has been ripped. If you've ripped most of your earlier CDs on the B2, and started downloading some of them recently, that would account for the difference.
Don't worry about it.