Why does part of multiple folder end up in albums the rest in playlist?

This I don’t get.I sometimes have problems with screwed up tags etc but I downloaded a folder with 6 sub folders.Then used secondary player (WMP11) and used “add to play list” and way I normally add multiple folders “play” and then “add to to library” (F3) and what’s weird is first two CD’s end up as “artist” and “album” but only first two CD’s plus a song or two from third are there.Under Playlist all 6 CD’s are there except first (one or maybe two).Next to artists it say’s “five hours plus”.Why aren’t they all in main library list?I did not ask WMP to make play list and am surprised two CD’s load properly the rest in play list.Any ideas?