Getting limited song-radio results

Hi all!

I was listening to Spotify today, when I noticed a song radio I made was only playing two songs (the song and another song from the same artist), so I came to check it out. The song was released very recently (within a week or two).

I replicated the radio with the Echo Nest API using this call:

http://developer.echonest.com/api/v4/playlist/static?api_key=API_KEY&song_id=SOUTLZJ14A7E01803B&format=json&results=20&type=song-radio

Is there is a time buffer for new songs to be linked to other similar songs? Is there any better way to be getting similar songs?