qfsyd,

AFAIK, QF sell I class on such a basis as you are referring to, 'once in a blue moon'. I do not believe QF yield management makes a habit of opening up I inventory once sold (if any were available in the first place).

FWIW, There will generally be D class before I class. Also, if you see D7 I3 and book one of the D seats, it will then go to D6 I2.