Omg. I think I figured out why there are two John Lockes. I can't believe that I didn't think of it before. I'm sure it has been mentioned, but I haven't heard it. So, if it has been mentioned, sorry.
So, according to Ben, no one has met Jacob. He is some magnificent man that everyone answers to but no one has met. He has been there a long time, and whether he is a god or a time traveler, he knows the future.
We know that Jacob met some of the losties, some when they were children, some when they were adults.
I think Locke met Jacob sometime when he was on the island and recognized him as the man that helped him after his father pushed him out the window. Or maybe when Locke met the smoke monster, Smokey showed him memories and one of the memories was Jacob helping him. Anyway, Locke recognizes Jacob when he meets him on the island.
I think Locke and Jacob are working together. I think they met and came up with a plan (kinda like Dumbledore and Snape)for Locke to kill Jacob. How are they gonna do that if John is dead? Time travel!
There have been other instances (like when Sawyer sees Kate helping Claire give birth) when there are two of one person on the island.
So, I think Flocke is really Locke time traveling to the future to help Jacob. He would know that he died and how from Jacob.
I don't like the idea of Locke being the bad guy, so I said he was in cahoots with Jacob, but it could also be that he is working for MIB, also. Either way, that could be why there are 2 Lockes.
Like I said, I don't know why I didn't think of it before and I am sure I am not the first person to think of it, but I haven't seen a theory like this on this site since I have started reading them. Please lemme know what you think.