I have hard time understanding Postgresql OVERLAP function when provided Interval
As far as I understand it, (DATE '2001-02-16', INTERVAL '100 days') is evaluated as (DATE '2001-02-16', DATE '2001-02-16' + INTERVAL '100 days') 

Which in turn is the same as (DATE '2001-02-16', DATE '2001-05-27') and that obviously doesn't overlap with (DATE '2001-10-30', DATE '2002-10-30')