Discount dates have not yet been released past Jan, 03. That's why you can't book with the discount as of yet.
I would expect the dates to be released early fall, but, there's no way to be sure.
You can book now, at the lowest rate and adjust your rate when the new dates are released, or you may choose to wait until that time to book.
Check Glo's FAQ (anchored at the top of the page), because that's where the new dates will appear, when released.
SwanDolphin (at the resort) sends the dates directly to her, when he releases them. She's the best source of SD info on here.