Missed this thread before while I was out of the country, or I would have replied.
With Diamond you need to keep in mind the distinction between ownership and Club membership. You can't be part of the Club unless you have a club ownership, but you can own without being part of the Club.
When you are a member of the Club, you can have full access to the entire Diamond resorts system. That includes all Diamond Resorts as well as affiliate properties. Also Club membership includes an Interval Gold membership as part of the club dues. I think that's pretty straightorward. One wrinkle to keep in mind is that if you are part of the Club you can only book reservations through the Club; you can't make a Club reservation and deposit that reservation with an exchange company.
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It's a bit more complicated if you have a Diamond ownership but are not part of the Club. In that case, you will either own an interest in one of the Club trusts, or you will own a deeded interest in one of the specific Diamond resorts. If you have a trust ownership, you can reserve at any of the resorts that are in that trust - that's like a internal trading system, but only for the resorts that are part of the particular trust that you own. If you have a deeded ownership at a specific resort, you can only reserve at your home resort, in accordance with whatever the reservation rights are for your deed.
If you are not in the Club, you can make a reservation and deposit with an independent exchange company.
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Finally, Club membership is not transferable, so if you buy a resale unit all you only get a trust or deeded ownership, as the case may be. To get into the Club you have to make an additional purchase from Diamond, and then your both your existing and new memberships can be brought into the Club.