There can be a lot of wait list fulfillments at the time an item begins to ship, because of last minute cancellations and credit card declines. That frees up some pieces to those on the wait list.
After the initial shipping period has passed, there is still a chance that your wait list order might come through. I would imagine that after the 30 day return window for all orders has passed, any pieces that were being held back for returns or replacements could potentially be freed up, allowing for a wait list order to be converted. And there are times when they find a few boxes in the warehouse long after an item has shipped, and that can also lead to happy wait list customers. (Although this probably isn't an intentional process of meaking people sweat it out--they really do just find them sitting on the shelves in the back next to the crate with the lost ark.)
I have personally had some good luck with the wait list in the past, getting such items as the Exclusive Han Solo PF, the exclusive Iron Man Comiquette and the Exclusive X-Men VS. Sentinel diorama--all three of those orders were converted after the items had already been shipping for a while. There have been many other examples of wait list orders for long sold out items being converted, so there is always hope!
The newsletter each week will tell you if any particular wait lists are being closed. Once that happens, you are officially out of luck, but until then, you can always have a little hope. For example, I still have a wait list order for the Treebeard bust sitting in my account. Until the wait list is closed and your unfulfilled request gets cancelled, you shouldn't give up.