To answer the question further, say for March there are 15 green lines and only 10 green FOs.... there will be 5 left over green lines that can be awarded to non-green pilots. Which ones will be available all depends on whether or not all of the green pilots actually submit a bid. (if they all bid for the last 10, the first 5 will be available; if none of them bid, it'll be the last 5 that are left over). They seem to be good at designating the right number of green lines, the only thing I can think of that would screw it up is if someone didn't pass IOE by the time they needed to for that bid.

That is my understanding, anyways.

A few months ago when it mattered for my bidding, I'd always throw some green lines that I would've liked onto my bid in the chance that they wouldn't get awarded. (just make sure you bid on enough non-green lines to CYA!)