Honestly, if you can still make sense of this you're doing a better job than I am, as IGN reports BioShock 2 will not have the Sea of Dreams subtitle, which was earlier dropped before being reinstated. Why? It was the name of the trailer, apparently.
"We name most of our trailers at 2K and the name of the teaser trailer we released last October for BioShock 2 is called 'Sea of Dreams,' 2K spokesman Charlie Sinhaseni told IGN. "There was talk about adding that as an official subtitle, but we decided to simply keep it BioShock 2. We're sorry for the confusion, but we're glad people are so interested."