I was taught that eilu v’eilu is an actual halakhic status. Even in a machlokes in metzius where one is wrong, eilu v’eilu means that you are yotze limud haTorah by learning that opinion.
Sam2: An indeterminable historical fact counts as eilu v’eilu, not because it’s a machlokes in metzius, but because there is no hachra’a so there is no reason to say that one is right and one is wrong anyway. Where there is sufficient evidence to make a serious case for both sides, IMHO it would be a machlokes in metziyus even if neither side has incontrovertible proof.