Auto update playlist, where did original songs go?

[HansPatat]

I'm am following a Playlist (3FM) which is automatically updated every week. I've synced the playlist to play it in offline mode. I wonder, where do the songs go which were in the playlist the week before the update? I found out that the songs still remain synchronized but can't seem to find them when the new playlist is synchronised. 

The playlist contains 30 songs and every week the songs will be deleted and new songs will be featured in the playlist. Where can I find these deleted songs? They remain synchronised on my iPhone.

Iphone 4S, iOs 6.0.1