Zardnaar
Legend
No, Athas was always part of the 2E metasetting, just hard to access.
Its why I said originally. In early DS products the Athas cosmology was different as its elemental planes for example were wrecked. They sorta added it to the Great Wheel later in non DS products (Planescape IIRC).
To get there you did not have to planar travel but dimensional travel to get from the great wheel to Atha's cosmology although the Athasian and GW Astral plane may have been semi accessible.