"If crew repositioning granted those four employees "must ride" passes, could United not make the argument that those four seats were then not "available" per t

"If crew repositioning granted those four employees "must ride" passes, could United not make the argument that those four seats were then not "available" per that definition? " No. Because by the point that happened, they had ticketed, confirmed, and reserved all of the space. By definition, it couldn't be confirmed and reserved space if they had reduced the number of available seats ahead of time, but they didn't. They marked everyone else as confirmed and reserved. There is no provision for changing the number of seats after the fact. The number of spaces on the flight is actually fixed ahead of time, again, by law ;) This is why united's contract of carriage says: "A reservation for space on a given flight of UA is valid when the availability and allocation of such space is confirmed by UA and entered into the carrier’s reservations system. " Note: ahead of time. it continues: "Subject to payment or other satisfactory credit arrangements, a validated Ticket will be issued by UA or the authorized agent of UA indicating such confirmed reserved space provided the Passenger applies to UA or the authorized agent of UA for such Ticket within the Check-In Time Limits" and " Once a Passenger obtains a Ticket indicating confirmed reserved space for a specific flight and date either from UA or its authorized agent, the reservation is confirmed even if there is no record thereof in UA’s reservation system." There are no provisions for undoing this. At the point they confirmed it at check-in, it's confirmed and reserved, period. No takebacks. Further, there are no provisions for "must-ride" tickets in the contract of carriage. They can't even make the argument they gave them zero fare tickets. The CFR, again, says " A zero fare ticket does not include free or reduced rate air transportation provided to airline employees and guests." They pretty much have no way out of this.