Not true. $25 confimed cannot be used when a flight is overbooked, booked even, or underbooked by one seat, no matter what the fare class availability. Flight must be underbooked by two or more and H or lower available. In practice, I think H or lower will always be available whenever the underbooking condition is satisfied.

That was my point. Nothing you do on a small scale is going to make the flight more underbooked; the only thing you can do is to book extra seats, and that won't help you. In cabins where they don't overbook, you have more leverage, but it is unethical for sure and almost certainly a violation of the CoC.

Charles