Makes me wonder how many more songs from DS and MK solo are still lying in the vaults...?
I often think about that too:) But no one has more than Bruce Springsteen. 
According to Ed Bicknell's various Q&A, he said there was very little or nothing DS-related left in the vaults. I think he's said on a few occasions that they were always scrambling to find material for b-sides etc so I don't think there will be anything other than maybe some very rough demos of songs that never made the grade and
shouldn't be released.
MK solo has been much more prolific it seems in terms of songs so there might be some gems there, although most albums have come with a number of "bonus tracks" so I suspect that again, anything that is releasable has been released and what's left should remain in the vaults.
