Newbie needs help understanding how this works

I just signed up and wanted to see about a rental in Vail Colorado in January. What is confusing, is they all seem to indicate there are rentals available at Marriott Streamside with sites of Douglas, Evergreen, Birch. Virtually all of these indicate the unit is "unassigned". I am assuming that Streamside is the resort, and Douglas, Evergreen and Birch are specific sections within "Streamside". I know when I lock in a week with my Marriott timeshare, I will know which specific location my room will be. So, my questions: 1) how is it that people are offering up a specific week, yet showing it as "unassigned" (which I take to mean I could find myself in any of the 3 sections, which might not be what I want); 2) IF I want to ONLY consider, say Douglas, is there a way to do so?

If they booked using Royal Holiday points the unit gets assigned by the resort. Many resorts are not fixed week fixed unit so this not unusual or cause far alarm. Ask the person renting the unit.