Marriott's two systems, Weeks and DC (soon-to-be-Abound) Points, have separate reservation rules and Reservation Window/Inventory Release dates.
For Weeks: Each resort has its own Seasonal Calendar and its own check-in days of the week. Examples: Platinum season at a resort at Hilton Head Island is generally only the summer months while Platinum Season at the Hawaii resorts is generally all year long, and, most of the resorts at Hilton Head Island allow Weeks check-in days on Fri-Sat-Sun while the Aruba resorts allow Thurs-Fri-Sat-Sun-Mon check-in days. Owners of multiple Weeks can use the 13-mos Reservation Window to book any combination of multiple Weeks, or multiple lock-off components from multiple Weeks, when booking consecutive/concurrent stays, with the Release/Call-In date being 13-mos in advance of the first allowable check-in day of the first reservation desired. Owners who are booking a single Week can use the 12-mos Reservation Window, again with the Release Date being 12-mos in advance of the first allowable check-in date of the desired reservation. (It's not as confusing as it sounds, and, there's a tool on the website where you select Weeks usage then input the resort and the date you want to check-in after which it tells you the Call-In Day for each Reservation Window.)
For Points: Reservation Windows are determined by a DC Member's status, which is determined by the total number of Points which the owner has purchased and/or the total number of Points for which the owner can exchange enrolled Weeks. The top line of this "
Benefits At A Glance" chart shows the number of Points required for each status tier, and, the second line shows the Reservation Windows depending on the number of nights of a desired stay. Again, the tool on the website makes it very easy to know the exact Release Date.
Weeks and Points inventory is not released on the same day, so the 13-months Release Date for Weeks usage is not the same as the 13-months Release Date for Points. Some Marriott owners know which days of the week each is released but I find just using the tool and not having to remember all the details is so much easier.
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But when all is said and done, regardless of which DC/Abound Reservation Windows you're eligible, like every other exchange company ALL reservations are based on availability. If there are vagaries which should prevent Marriott from releasing inventory for reservation confirmations, I would expect that Marriott won't release it. And as has been said by so many others, nothing can be made available via the exchange company until and unless the owners (including Marriott for any intervals it owns, or any inventory machinations it's entitled to make) elect to exchange for DC/Abound Points. When that election is made with an enrolled Marriott Week it cannot be reverted back for any other usage, and I'd say it's practically a guarantee that the same will be true with Vistana elections.
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Just want to say I don't want to be cluttering your thread/forum with unwanted info, and I know that my book-writing style isn't everyone's cup of tea. Know that I'm happy to sit and silently watch if that's what any of you need me to do - just say the word.