There are zero provisions in their contract of carriage for must-ride (let's ignore this), but more importantly, they cannot change the amount of confirmed and reserved space after they confirmed and reserved it at check-in.
There are no provisions for unconfirming and unreserving, by law.
So sorry, if they tried to confirm and reserve tickets for the crew, "must-ride" or not, after they checked in the flight as full (not after they boarded it), they would still be screwed. Denying boarding would still be breach on their part, because the flight would not actually have been oversold. This is because they could not have validly confirmed and reserved a seat for their must-ride once the flight is fully confirmed. Period, full stop. They could only reserve one (and worse for them, https://www.law.cornell.edu/cfr/text/14/250.2a says those people, the must-ride, would be the first to go).
They don't get to just mark all the tickets they like confirmed and reserved and remove other passengers.
Otherwise, these provisions would all be meaningless :)
They cannot actually validly confirm it unless their is actually space on the plane. The only case this occurs otherwise in practice is an accident (IE ie system screwup assigning two people, same seat). Otherwise, they just don't confirm them until you get to the gate, and you are holding a reserved but not confirmed (I believe that is the correct way, and not the other way around) ticket.
This also means, as you might expect, most of their "Oversale" situations are not really oversale as defined by federal law (and they can't really deny boarding for them). They are really "we issued more reservations than we can confirm for this flight". and they would like to get to confirm everyone who really wants to go.
This is how they avoid most of the issues in the first place.
That's also particularly why when those people go to check in, they don't confirm and issue reserved boarding passes.
They tell them to see the gate agent. Because they have not actually confirmed the reserved space :)
So it's only actually oversold if they just issue confirmations to everyone who checks in, instead of not actually confirming :P.
That's why it's confirmed and reserved (for that specific passenger/flight/time/seat) and not "kinda confirmed and kinda reserved".
If you actually follow the flow chart steps the contract of carriage lays out, and compare it to with what the CFR says, they are pretty much out of options.
Now, they certainly would have done it anyway, but they would still lose the lawsuit. Again, by law, at the point they have confirmed and reserved all the seats, their only actual legal recourse is to find volunteers.