There's an interesting article I was reading not too long ago about playlists (A/B/C list, BBC Introducing etc) and also how they playlist older songs into "Recurrent", "Silver" and "Gold" lists. Worth a read (if you haven't already seen it) for anyone interested. http://www.bbc.co.uk/programmes/articles/1jJsyK6Vt5x3JQgycD9xhdW/heres-how-your-favourite-music-makes-it-to-the-radio-1-playlist