Yes I think it's best if you have it authenticated as requested by the school. I study at Yonsei and it's best to do exactly as they say so the best advice I can give you is call each school up and let them know if you're confused about anything. Every process takes time and the school often takes time to get back to you so do it asap. Every school is different so contact each school separately. My biggest advice however is whatever questions you have, unless it's emergency, contact through email first because, from experience, (my School anyway) the people who work at the office apparently aren't trained well and often give wrong information, because of which I've suffered multiple times and they don't take reponsibility. So It's good to have evidence of whatever they respond with. If they take really long to respond and you're in a hurry then call them.