I’ve got one theory. There were 324 people on Flight 815, according to the Oceanic 6 there were only 8 survivors. 324-8 = 316, or the number of bodies that would need to be on the plane that was “found” in the trench. However you would imagine that Widmore would have put 324 bodies in the plane because he didn’t expect/want any of the survivors to get off the island. Is that what 316 refers to? Guess we’ll have to wait and see.