In LA X Jin and Sun are not wearing rings and Sun is referred as Ms Paik. Many have said that they're married in this timeline, saying "Why would Sunbe treaveling with Jin?" "Why is Jin delivering the watches?" "Why does Jin tell Sun to buttom up?" the answer to all this is Mr. Paik. Well on flashbacks we see he approves the marriage if Jin works for him, I think that in this storyline Mr. Paik basically says "Sure you can marry my daughter, but first you have to work for me for x amount of time, so I can see you are trustworthy". This would mean that Sun & Jin are not married, yet. They could get married in the future. Or they're going to LA to get married, escaping form Korea (my personal favorite). If they are escaping is similar to the purposes they had in WHH, and remember the producers said that the characters have similar ambitions and reasons for being on 815.