I was trying to help a friend reserve a Memorial week using her Marriott Horizons Platinum week. I was told that she would have to deposit her week with II and then exchange back to her same resort for Memorial Day. Doesn't this sound ridiculous? Why shouldn't a platinum be able to reserve in Gold. In any other timeshare if you are platinum you have the whole year to chose from.
Most of the other systems that I'm aware of that allow this also have a home resort reservation period where only owners at that resort, during the season they own, can reserve a week. After the home resort period ends then it's open season for anyone to grab a week, either moving up from a lower season or down from a higher season.
Hilton, for instance, grants home resort advantage for 3 months. At the 9 month mark anyone can reserve whatever inventory is remaining. With DRI the home resort advantage is only 2 months. Both of these are points based systems.
Marriott remains a weeks based system. You own in a particular season and can reserve a week only in that season. Since it's a weeks based reservation system, you must exchange one week for another if you want to stay in a different season.
In some ways, points based reservations systems are similar. You have to wait until the home resort reservation period has ended and then, if the owners in that season have reserved all the weeks available, you can choose from what's left over.
IMO, points based reservations systems are more user friendly. They allow for movement between seasons you own in, assigning higher values to more popular seasons. Of course there are pro's and con's to both systems but, in general, I do prefer the flexibility offered by points based reservations systems. However, that's not how Marriott handles reservations for owners. So your stuck in the season you own unless you want to exchange. I would suggest making a reservation in Platinum season and then doing a request first interal exchange. That way the owner doesn't turn loose of their week unless there is a week available for exchange.