Maybe they've not gotten as far with your processing as they have with others? If I click through "Manage My Account - My Profile" then the screen that pops up has different boxes. Top to bottom is:
"Marriott Vacation Club Webuser Overview"
"Communication Settings"
"Marriott Vacation Club Customer Account Detail"
and, last, "Interval International Account."
If I click in the bottom box, the II Account box, that's where I get the same little pop-up that you see and it re-directs to II if I click on any weeks. But the third box - the Account Detail box - is where you should be looking for the new II (and DC) account numbers. Mine is split in two sections with info for Don and me, with most info identical except each name shows different account numbers.