Once the dust settles and most of the hand wringing dies down on this contract, one thing you should not allow to get lost in the shuffle is; Who is the NMB and what is their real power?
There has been a lot of discussion on what they will or will not allow or how they would judge this or that, a lot of which is pure unadulterated balderdash. They can and will be anything you let them be, through acquiescence, ignorance or assumption.
I believe you would be wise to form a committee or some such, while you have the time, to look into their mission and their actual powers to separate the myths from the facts. Granted, over time these have been heavily influenced by political evolution but this is a contamination of the process not a definition.
This of course is something the International should be doing but …
Next time you sit down to negotiate a contract you won’t have each other to blame. Labor negotiation is by definition an adversarial relationship and you will, at least fall short, if you don’t know and understand your “adversaries”.

Disclaimer: I am retired. (and old)
and by the way Congratulations on having a "joint" contract.