Originally Posted by
NYC2SGN
My understanding was that you only needed to pay a fare difference when you're changing your ticket to a higher fare class. I called back to ask another agent and the second agent said it's possible to still have to pay a fare difference when you're changing a ticket and the new flight(s) are the same fare class. The agent said I was originally scheduled to leave on a Tuesday, and now I am leaving on a Sunday and "fares on the weekend will always be more expensive than fares on a weekday [even in the same fare class.]" I know there are multiple fares that are filed with the same fare class, but I don't know if that even factors into fare differences when you change your ticket. Maybe I'm confusing ticket changes with SDC, in which the fare class rule applies?
The second agent was correct, and you are indeed confusing slightly with SDC, which technically should be the same but (a) you usually don't SDC to a different day; it's literally "same day" change, and (b) the way SDC is coded and usually handled, the standard rules check is ignored, probably because as originally envisioned you would not be doing an SDC in a way that could break your existing fare rules.
It's extremely common for international fares to be valid only for certain days of the week, usually with two schedules: W (weekend, higher because business travel usually isn't on a business day when int'l) and X (the other one). For EWR-HKG, template W is for travel Fri/Sat/Sun and template X is for travel Mon/Tue/Wed/Thu in each direction, and the templated fare difference is $50 half-round-trip. Usually, but not always, the same fare family has an X and W version for the standard difference.