Do you have a specific iTunes Music Library folder on your hard disk drive?
Are the songs still within this folder?
Do a computer search for terms .mp3 & see where each is located.

With LW 5, songs can be auto-copied to LW's music library as soon as the songs are 100% downloaded. You will see this setting under LW's menu bar, Tools -> Options -> Downloads.

If songs are already in iTunes Library, then any iTunes updates should not affect them. Such iTunes updates should also not affect any playlists such as the LW playlist/LW lan listing.

You referred to LW Library. I'm guessing you mean the LW listing under the playlists. This is a listing for use over a LAN. Go to iTunes menu bar, Edit menu -> Preferences -> Sharing, & make sure Look for Shared Libraries option is checked.
Open LW, go to Tools -> Options -> Advanced -> Files, check the option Share the audio section of My Library on my local network using iTunes. You will need to restart BOTH LW & iTunes before this has any effect.

If you are using LW 4 then Tools -> Options -> iTunes -> Sharing, & check option. You may need to uncheck, press apply, then check again & press apply. Again, need to restart both LW & iTunes.