Silvertear falls is regulalrly discussed with references to its aetherial importance to Eorzea, not Hydaelyn.

It could stand to reason that it is only the centre point for the aether in Aldenard and that the other continents thus have their own localised networks. This would explain the presence of primals outside Eorzea that the Empire has encountered.

Although I'm still stuck on the one that appeared in/around Ala Mhigo, a part of Eorzea/Aldenard. It wouldn't be Midgardsomr since Midgardsomr is not a primal.