Ok, there' a version of Sun, who never crash on The Island. She's at LAX airport, now, waiting for Jin to be released. I name this version of Sun: ALTSun.
Then, we have a second version of Sun - I name her RealSun - actually outside the Four Toed Statue with Lapidus, Ilana and the first group of The Others.
But we have a THIRD VERSION of Sun. Where does this OtherSun come out form? The same ol' story: Ajira 316 flash in time. When Ajira 316 takes off from Los Angeles, it's January\February 2008. When Ajira 316 crashes on The Island, it's the end of 2007. So, the day after the crash of the Ajira 316 on The Island, we have THREE VERSIONS OF SUN: one is in the alternate reality, one is on The Island, one is in Korea making her business or in London talking to Widmore or in LA talking to Kate.
What's wrong with this? It seems more than logic to me.