To further clarify:
Worldmark owns some units at Eagle Crest, in Redmond, Oregon. Those units are part of the Worldmark system.
There are other units at Eagle Crest that are part of a standalone timeshare. They have the season and MF setup as described in the OP. Sounds like that's what this is.
Worldmark owners may exchange II- or RCI-rated timeshares (Gold Crown, Premier, etc. - I think EC qualifies), that have been deposited into II or RCI, into WM for WM credits, at a per transaction exchange fee of $129. In exchange, WM puts about 80% of their equivalent credit values into the owner's WM account. These credits have one-year lives, compared to normal WM credits that have 2-year lives.
So one must be a WM owner to take advantage of this. But WM owners who are also EC owners say that the best value of EC is to exchange through II.
Here are more details for this Exchange Plus program:
http://www.wmowners.com/forum/viewtopic.php?t=6079
A red 2BR at WMEC costs 10K credits. White season costs 7K, and blue 5K. The MF for 10K of WM credit is $608. The buy-in cost is about 40 cents per credit. Red Season at WMEC goes from April to October, plus holiday weeks/periods.