Windows media player is probably insisting on using metadata tags instead of filenames to identify the artists, albums, and tracks. When the B2 rips a CD (using a CD drive attached to or internal to the B2), IF it finds album information it applies a minimal set of tags intended for use with Sonos. If it didn't find album information and you renamed the ripped albums/tracks later, the B2 does not have any information to put in tags and it doesn't add or change them when you rename.
How did you get the music into the B2? Did you do something different for the 77 albums that are identified, as against the ones that aren't?