Um as I recall the first union proposal we saw had 2% retro. Full retro was deemed outside the "zone of reasonableness."
I can see where gunga din is coming from as the laymen's understanding of negotiations is start high, counter low and meet in the middle. From what I see the work rules/hos remain current book-maybe that's where the majority of the back and forth will go; i.e.-change this rule pay goes up xx.