Yeah, it may very well be on the shelf waiting for a better release moment, or to go as bonus track in a best of CD or to be released after the artist passes away unexpectedly and the heirs want some extra inheritance. Well, you get my drift.
Technically it’s not allowed to alter tracks (released or not) without specific written permission. You don’t buy music, you buy the right to listen to it for personal benefit. It remains property of the author though.
With unreleased songs you have to wonder: where did they come from. It could actually be stolen, at least with a released track you’ll know it was supposed to be out in the open.
I’d be real careful with reuse with your name pasted on it. Obviously if you are playing an obscure 30-people house party, I don’t think you are gonna get in a lot of trouble. Playing it in front of thousands at the ministry of sound might not be a very bright idea (but should be doing your own thing there to begin with 🙂 ).
Greetinx.