With an unused rebookable (no fee) ticket (Plus/Business Smart to US) how is the fare difference determined?
A. Is it always direct price difference, i.e. price of new flights minus price paid?
B. Or is it class based, so as long as I find another flight in the same fare class (e.g. A or J) it's free?
C. Something else?
(Need to call to change and want to find the best new dates.)