Apologies if this is a stupid question, but I wasn't clear from the wiki:

If I have a 3 segment flight, I know I can SDC via A at t-24, and that the fare buckets equalize for the first segment at t-3. I am assuming that if I'm in a G fare and the available fares are Q and up, that even if there was space in the first segment at T-3, I would still have to pay the fare difference for the later segments? Or would a helpful agent be likely to overlook this?