Originally Posted by
Blank Sheet
4) The purchased fare class must be available.
Nope. That's not true for invoking this rule.
The whole point is that a lower fare class could open up (e.g. you go from 'L' to 'K').
When you're using this rule, you are basically doing a ticket exchange and being booked into the new fare class. Technically, the fare class could be HIGHER than the one you originally purchased but the fare is lower.
The only purchased fare class that has to be available is the "new" one you're attempting to get in to...but then you wouldn't have found the lower fare in the new fare class if it weren't available for purchase anyway.
-RM