So I hadn't seen if someone had already explicitly confirmed this, but we did have successful price-bridging this past week from pre-10/16 MYW tickets (purchased at
UT) to new Platinum APs. My 6-day PH MYW ticket was upgraded on first day of our trip (10/18) at Guest Relations inside of Epcot main entrance, and the CM hit my expected price right on the first try. They properly gave me the full gate pre-10/16 price versus current Platinum AP cost.
We upgraded my wife's ticket at AK on 10/22, at a random "ticket stand" near front of the park (staffed by just one CM). The first price he quoted was wrong, seeming to be ~$20 too high, presumably by crediting me the online price instead of gate price. When I told him that didn't sound right based on my prior experience, he tapped my Magic Band and was able to see the full history of my upgrade and the right codes to use to replicate it again for my wife.
I was also able to use a discounted Disney gift card brought with me to pay off the upgrades on each, so all my original savings were generally still intact. Still a little bummed that we paid essentially $50 extra per AP because of the 10/16 price hike 2 days before our pre-planned upgrade, but the pain at least stopped there, and still came out ahead overall with the UT savings.