Mike Dirnt of Green Day talked with Music Feeds about all the unreleased material the band has stored away:

We have so much stuff, and some of it has morphed into other songs, you know, a song that took 10, 20 years to evolve but started off as a jam or started off as us singing a different lyric to it or whatever. I mean, there’s little opuses in other songs and things like that we’ve done that people have never heard.

And:

I don’t know when they’ll see the light of day, but me and Billie always said ‘at some point everything comes out in the wash.’ So, you know, at some point it’ll all come out. We’re not in any hurry to do that because this band has never really been in the business of looking backwards. Maybe some day when we’re older, then we’ll look back.