That is exactly what they said in the TA, though it wasn't really necessary to state the obvious. Neither ALPA nor the Company, the bargaining parties, can unalterably relinquish their right to freely change their mind about their bargaining positions throughout the whole process. The notion that the company must be in fear of liability, to any subgroup that has no direct power to bargain, while the bargaining proposals change at every whim, is obviously contrary to their right of both opponents to freely bargain. Each is liable to those they represent. Otherwise you suggest each bargaining rep is liable to the opponent's subgroups, which are simply a part of the collective group they hope to profit from. And this despite the fact that they have no legal ability to bargain with a subgroup, much less even a responsibility to bargain on their behalf. Being able to freely bargain necessarily includes the right of each bargaining opponent to advance its own interests at the expense of the other.
If you sue the company and the union for agreeing to a grievance settlement that you don't like (think PHX crew news), then it is pretty obvious the company would be quickly dismissed from the suit, sorta like what happened with Addington.