With my II account it shows all the possible weeks I could deposit. I used to own two timeshares that I could deposit into Interval. Even though I no longer own either one of them, they both still show as available for exchange.
So unlike RCI, I could actually start an ongoing search with those weeks that I don't own or haven't deposited. However, when there's a match, II will deposit those weeks and verify the deposit with your resort. Of course, my exchange wouldn't go through as the week wouldn't be verified.
Presumably you must have given them information about the week you own when you opened your account? How long ago did you open your account? When you go the Exchange tab on the home page after signing in, there should be an option for "My Units." That should show all available units whether they've been deposited or not.
So the big difference between that and RCI is of course you can only search in RCI with units you've actually deposited.
I hope my explanation isn't too convoluted.