Upon purchase of a week (you get a fee simple deed), the buyer agrees the deed to the week is to be deposited in a Mexican trust. The Mexican trust has Mexican nationals (bankers) as trustees and holds legal title to the trust assets (the deeds). The trustees administer the day-to-day affairs of the trust. The trust administers the right to use granted in the deed for the benefit of the owners of the weeks sold.
The trust expires in 50 years and may automatically be renewed for another 50 by the trustees. Not at home so I don't have easy access to the original documents I received. So, this is all IIRR.
Despite the questions raised in the linked post, nobody has claimed to have problems transferring title at Lagunamar. Salty