Not to keep beating a dead horse, but I would like to put forward a couple of example scenarios to contrast "taken out" vs "concession", both for general edification as well as to check that I have it right.
Lets assume I start this exchange with a 4 box stress track, no stress and no consequences.
BBG is winding up and looks like he will lay a major smack down on me.
I don't think I can proactively concede at this point because I have not taken any consequences, although it looks like I might be able to negotiate a consequence as part of the concession if everyone at the table feels it is reasonable. I would need to do this before the attack is rolled.
Lets say the guy hits me for 8 stress. Now I know that the real boss BBG is still to come so I don't want to go in to that hurt and I don't think this guy is trying to kill me, just put me down. I could choose to be taken out right now and not suffer any consequences at all (at the risk of whatever "taken out" narration the GM chooses to impose).
I could take consequences, stay in the fight, and then clearly have the option to concede in the next exchange if I want since I have taken consequences.
Clearly not a very macho character, but does this capture the RAW?