But this is simply untrue. Vistana (which "owns" WVC and SVC, which aren't companies but just brands) is not owned by MVC. It's owned by Marriott Vacations Worldwide, which is the company that owns both MVC and Vistana. Putting it another way, Vistana is NOT under, or a part of, MVC. They sit side by side in the corporate hierarchy and are separate (but related.)
I got double elite nights for my WKORV stay last month and I fully expect to get them again for my WDW stay that begins tomorrow. If I don't I will complain until I do. They can't just make up rules on the fly.
Now — if your stay was through II, I'm not sure if that qualifies for elite night credits at all. But ownership stays within VSN do.