The key document that needs to be filed before sales can legally begin is the Declaration of Condominium, a very long document that you get at time of sale. In the past, sales for resorts that had pre-opening sales usually began within a month after that document was filed. The earliest we have seen a declaration filed was with BLT, about a year before the resort was scheduled to open (it ended opening a month earlier than projected). Contrary to what some may believe, there is no law that sets a maximum time before opening, such as a year, when sales can begin. However, the laws are designed to make it impracticable for the developer to begin sales a very long time before completion. For example, if the projected resort opening is delayed, pre-opening purchasers could rescind their contracts. Also, Disney cannot sell an initial use year that could run out before the purchaser could use the resort, e.g., it would be improper to sell a December 2016 use year to start if the resort does not open before December 2017. Moreover, that Declaration that is filed needs to be accurate on what the resort will actually be, and thus safety dictates not filing it too long before opening because of a risk that a substantial change may be needed, which itself would give the purchasers a right to rescind.
So when it goes on sale mainly depends on when DVD feels comfortable that any opening date it gives will stick and no changes of signficance to the resort will be needed. With AKV, VGF and Poly, it took the safe course by starting sales 5 months or less before opening. With BLT, it went a little risky by stretching it to almost a year. When new WL
DVC was intially announced, the possible opening was projected for late 2017 or even 2018 but those kinds of projections made before construction begins are usually not what actually occurs.