I think Mark just has a musical 'box if bits' lying around. Short tunes, ostinatos, chord progressions, unfinished songs, etc that he can dip into when in need of inspiration. I can think of numerous bits and pieces that have been reused and repurposed. Off the top of my head, PI outtro on news, Secondary Waltz and its several iterations, No can do riff, I'm sure there are more examples....