The last non-concessionary contract I was able to vote on (COEX C'97) had "full" retro for pay rates only. No added $$$ for the other items that cost us money.

So in that sense "full retro" has happened and it can happen.
But the longer it drags out the more likely that 50.1% will jump at whatever scraps are offered while the execs count their millions and laugh at the pathetic fools they screwed over yet again.