Дейв спойлернул. Наконец-то официальный ответ: Аркадии разные.
In first edition, it was up in the air, but in second edition our decision to make the Supernal World what you see when using Mage Sight, and the Supernal Realms the unseen Supernal without the shape of the world to give it structure, has made it much clearer. The Supernal isn't a physical place, it is a conceptual space, and this has a few other knock-on effects; first ed Geist and Changeling flirted (changeling much more so) that Stygia and Mage Arcadia were in the Underworld and Changeling Arcadia.
They're not. As of second edition, the "Arcadia Question" is answered with a great big No. The things that abduct people through the Hedge are not Supernal Fae, any more than the fuel Demons use is the Supernal World of the Obrimos. We considered the ramifications carefully, and decided that a long-teased crossover issue was an acceptable loss for the setting change we wanted.