The short answer is yes, it is possible to get credit for MVCI stays. I got credit for a stay in Park City and another stay in Canyon Villas in 2009. (Park City was a standard trade thru Interval International and Canyon Villas was on last year's Gift of Time offer, but I'd hope that this would apply for Friendshare stays as well.)

I saved the instructions on how to do this. Try the following. (I hope this still works - I haven't checked since they made those recent changes to the Marriott website.)

Hopefully you have some sort of confirmation certificate that shows the Marriott reservation number for your stay. (I found it on my Interval International confirmation.)

Log in to your Marriott.com acount and click the tab that says, "Upcoming Reservations." Enter the above mentioned Marriott reservation number and your last name. Then click "find." On this page you will see your Marriott resort reservation and room type.

Near the bottom, this page will also give you a link to "Add a Marriott Rewards Number" to the reservation. Click this and add your number. Your reservations will now show up on your Marriott.com account.

To be doubly sure, ask the front desk clerk when you check in at the resort if they can be sure that your Marriott rewards number is added.