Tracks dissapear from Itunes:why?

I just ripped 2 cds into Itunes library.One had 12 tracks but the library only shows 6.The other one was a double cd and on a second cd the library shows only 3 tracks instead of 12.Why this is happening?I saw all tracks being converted on the screen under the same artist name and now i cannot find them.Your opinions will be appreciated.
Sometimes they have different names once they are ripped. For example if you are sorting by artist, these tracks may have either a different artist or a different manner in which the artist is written.

Additionally and depending on what programs you are using for your ripping, sometimes what shows up for a song before you rip is different than what shows up after you rip. This results in some searching or you can go into the file with the library itself and search by date to find what you are looking for. Then you can rename the file to correspond with successful searches that result in the other songs from the same artist/album.