Let's keep calm here...
Myst: Where Releeshahn Maintainers’ marks were later added to Ages from the Myst, Exile, and Revelation:
Myst: Never added. The descriptive book was never moved from Earth.
Stoneship: On the telescope platform. Questions of jurisdiction are not fully resolved, however.
Channelwood: On the island, just outside the windmill. The area, however, is now administered by a surviving branch of the tree dwellers’ tribe.
Selenitic: Where the path from the rocket meets the path around the lagoon. Incidentally, by now the oasis will have spread at least as far as the clock and the rocket.
Mechanical: On the linking island, just behind the retractable stairs.
Rime: Near the hut, just to the right of the door.
J’nanin: By where the squee nest was.
Voltaic: (Or whatever the Age’s actual name was) Just across the bridge from the linking island, and to the left of the path.
Amateria: On the mossy island, across the path from the door to the turntable track controls.
Edanna: Swamp level, on the side with the nemel lotus root you enter in-game, but closer to the other nemel lotus.
Narayan: Never added. Narayan is independent, and relations with Releeshahn remain fraught to this day.
Haven: In the ruined linking structure. However, the Age is now a Pod Age.
Spire: Right in front of Sirrus’ sculpture of the scene from his childhood.
Serenia: Never added. Serenia is independent.