I feel your pain. Until I learned to differentiate courtesy levels in Korean, I had to beg the English team to illuminate me on what the characters were using.
Since then I’ve figured out a simple (not 100% accurate, but has a pretty decent percentage, good enough for most OL volunteers) to discern this by ear + by knowing what would be reasonably expected, given the Korean rules in society (those rules are the same in Chinese and Japanese society as well). I detailed it on a thread about editing (very good thread generally, highly recommended, many people said useful things there)
But … working at the subs without referencing the video? That’s a no no for me, if I find out a subber doesn’t follow the drama and watch all the episodes, I never work with her/him again. You are bound to make very stupid mistakes if you don’t know what’s going on, the character’s relationships, the backstory, to what they refer to when they talk. So more work for me the editor, just because of the subber’s laziness and greediness to take ten projects at the same time.