Everyone keeps doing the bloody maths between the albums but seriously, who cares? Just because that's been the pattern up till now doesn't meant that it'll continue. I don't think BJA sits at home having finished a song/album and looks at his calender going "Nope, gotta wait another four years otherwise the sequence will be broken"... :/
Let's do some calculations.
from 1039/smoothed outt slappy hours (1991)
To kerplunk (1992) = 1 year
From kerplunk (1992)
To dookie (1994) = 2 years
From Dookie (1994)
To insomniac (1995) = 1 year
From insomniac (1995)
To nimrod (1997) = 2 years again
From nimrod (1997)
To warning (2000) = 3 years
From warning (2000)
To American Idiot (2004) = 4 years
From AI (2004)
to 21sr CB (2009) = 5 years
Anyone see the pattern?
What if we get one in 2015?