Refs=0 means that they're not in any playlists. You can still use "search" to find them on the player, but they have been deleted from all playlists (or have never been added to a playlist in the first place).

Remember that it is possible (in 2.0 and later) to delete an item from a playlist without deleting it from the player. Back in the 1.0x days, deleting it from the last playlist was supposed to delete it from the player, so refs=0 usually meant something went wonky. Now it's a normal thing.