Mission Re-Do's

Just curious with Faction and Nightfall missions, should for whatever reason you not get masters on a run. Is it possible to re-do for the masters or are you stuck with whatever, standard/expert you first recieved.

You're free to re-do a mission again to try to get Masters/Bonus if you want. Except for the Doppleganger challenge at Augury Rock, that one you're stuck with your result (as far as I know, unless they changed it of course)

If it's still like that, it would be impossible for some people to get the Protector of Tyria title because the Doppleganger battle and bonus both count for the title even though it isn't displayed in the title. And as far as I know, the only title you can fail permanently on is Survivor.

You can do it over and get the bonus on it, been that way for a while.

I am trying to find out about Masters after getting standard or expert in Factions or Nightfall.

Same thing as with Prophecies: you can go back in Factions and Nightfall and re-do a mission and still get Master's credit after you've gotten Standard or Expert's.