I have noticed that some songs are disappearing. There are artists that I am sure for 100% I have listened more then 100 song. For example Prodigy, Pitbull, Sweet Noise and more. Every year the number of their songs just decrease, slowly but decrease. I'm not sure if this have any influence for the main scrobble counter, because this changes are to few to notice, but I am totaly sure that I saw that every of this artist has more then 100 listened songs by me couple years ago.