Cindy, PPID is not inevitable. We don't know exactly why some horses develop PPID and other's don't. Certainly, it's been theorized that stress, oxidation, etc. contribute, but we don't know the exact mechanism. DDE +T will certainly help, and it's an excellent way of caring for your horse to avoid a multitude of other problems, including those not caused by IR or PPID.
I looked at your CH for Oden, in June he was still out of normal range for insulin. When you state swellings, do you mean fat pads? Fat pads are the last thing to resolve during weight loss and sometimes they never completely go away. Can you take a couple of full side view photos of Oden and post the in his album? We might be able to help you understand if he needs to lose more overall weight or simply wait on the fat pads to resorb. Also, if you haven't reviewed his diet since the June insulin reading, that might be in order.
Are you weighing his hay?
Dawn Wagstaff and Tipperary
Saline, MI 2003