It depends on what you consider as an ''unreleased song''.
If your song is published on Spotify and it can be listened by anyone, but you have not officially shared it with the public, yes, definitely you can promote it with us.
It will be possible because we have public access to the song's Spotify URI, which is the track's link that we need to send your song to the curators. Likewise, there will be no problem, as those curators will be able to listen to the track.
On the other hand, if what happens is that your song is not published yet or not visible to anyone on Spotify, then it won't be possible for the moment to promote it with us, because you won't be able to obtain the song's public Spotify URI.
Therefore we can not deliver your song to the curators.
You will need to wait until you can have the public Spotify URI so that everyone can listen to the song.
For more information about the song's Spotify URI, you can click here.
Note: sometimes you may have a URL, but if everyone can not listen to the song using it, it's not useful. You must wait until it is valid publicly.