Realistically the company is not going to go along with full retro pay if this ends up taking more than another 60-90 days. It's just too much for them to swallow. Go out there and find me a pilot contract with full retro pay signed in the past 10 years off of a contract that was amendable for 1+ years.

What your NC should focus on is getting a quality TA that doesn't sacrifice scope or quality of life for a little extra $$$ and one that includes yearly raises beyond the next amendable date so that the next time negotiations come up you'll keep getting yearly raises. Something like a yearly COLA+1% should do the trick.