I don't think that there ever was a ship programmed for 2012. At Some point after DCLs announcement Bernard Meyer basically said they had no ships planned for delivery in 2012. They have the capability to build up to 4 ships per year.
Usually when a line builds a ship, unless there's a specific reason for it to be a 1 off, they'll do a firm order for say 2 ships, with options for say 2 more. This locks down pricing, planning logistics etc.
DCL I'm thinking had solid order for 2, with options for several more. To date DCL has never exercised a ship option. With that said, the Dream class ships were 1.2 billion each. I can easily see the new ships at 1.5 to 1.7 billion each. So when DCL went lookong at financing it may have been better for them for 2 ships. But if the financial world changed, it could have secured money for a 3rd. As far the gap between the original 2 ships, it could have been the financing that DCL was using that it was in there best interests to skip a year, eother to help pay some back or some other reason. With all of the money that Disney ad a whole is dropping, they may have had some better leverage for better rates. It could even have been MW that did some wrangling with DCL for the 3rd ship.