Originally Posted by AnselmAdorne

Not to split hairs, but the 7 or 4 day window only applies if you were using an SSWU to upgrade from T+. An SE or E can now use an SWU to upgrade a Latitude fare at any time, whether a pass holder or not. If the pass holder decides to ignore a case of I > 0, they will still have a bit of an advantage in that they can upgrade from the usually larger J inventory, but only 24 hours before the flight. (And they get the 50% COS bonus too, of course.)

But to answer your question, no, I've never seen I > J or C.