Don't know the details but Miles left Columbia for Warners for the advance money. Miles had a habit of calling Columbia and asking for a $###,### advance on royalties and they sent bunches. At the end of the last contract Miles was into Columbia for something over 2 million. Warner's offered $XXXXXXX to sign. It was a "no brainer" for Miles and also a "no brainer" for Columbia to let him go.
Most deals for issuing new material involves the artist or estate. For example my Art Ensemble box entailed a payment to them of $xx,xxx for the unissued material.
On the other hand, with an artist like Miles and the bucks they were constantly throwing his way, the company probably has the upper hand but is reluctant to use it.