He must have unused songs from previous records to fill a double cd for sure, songs that are good enough but that they didn't fit with the rest of songs at the time (like Pyroman, Bonafide or Bonfire night) and don't fit with the music he does nowadays either, but would be good enough to be released.
It is a pity that songs that are good are left out just because they don't fit the rest and left behind forever.
I'm sure he recorded enough material for a couple of double albums in these last sessions and hopefully we would have the chance to listen maybe a 1/4 part of them between what it's in the record and the bonus tracks, and most of the rest would remain hidden just because they didn't fit.