Many resorts will allow you to deposit a year, possibly even two in advance. In order to do that online, Interval will always be showing units two years ahead as available for deposit.
If it's any comfort, I don't own timeshares anymore and Interval is still asking if I want to deposit the timeshares I did own at one time. If your question relates to units you've sold, Interval doesn't know that you don't own them anymore unless you tell them. As far as they know, you're just using them yourself.
Just be aware, of course, that deposits are verified with the resort before they can be exchanged again, so you've got to have your ducks in a row as far as your resort goes before you can deposit anything.
Actually RCI does the same thing. If you have an account with them and go into "Manage my deposit" from the Home tab, it will give a list of your resorts up to two years in advance.